1. National 4/5 Physics
In addition to set homework you will be expected to
finish off class notes and regularly review work against
the learning outcomes.
You will be expected to take responsibility for your own
learning and for seeking help when you need it. At the
end of each section, you must ensure all notes are
completed and examples attempted.

2. In unit 1 we will learn about the physics of motion.
We will focus on the language,
principles and laws which
describe and explain the
motion of an object. Kinematics, also known as Mechanics is the science of describing the motion of objects using words,
diagrams, numbers, graphs
and equations.
Print for lab books
The goal is to develop mental models
which describe and explain the motion of
real-world objects.

3. Key words: vectors, scalars, distance, displacement, speed, velocity.
By the end of this section you will be able to:
Describe what is meant by vector and scalar quantities
State the difference between distance and
displacement
State the difference between speed and velocity
State that force is a vector quantity
Use a scale diagram to find the magnitude and direction
of the resultant of two forces acting at right angles to
each other.
Tuesday 28th August
Initial lesson only 25 minutes with class moves etc

4. Key words: average speed
By the end of this section you will be able to:
Describe how to measure an average speed
Carry out calculations involving distance, time
and average speed.

5. Which of these are units of speed?
metres
gallons
miles per hour
seconds
minutes
amperes
miles
kilometres per second
miles per minute
watts
metres per second
Newtons

6. Speeds in….
In Physics we normally use units
m/s for velocity.

7. Average speed (m/s) High speed train Snail Sound 270 m/s 13.4 m/s
UK town
Fast jet
747 jumbo jet
10.3 m/s
29790 m/s
97 m/s
Air molecule
Earth in orbit
Falcon
60 m/s
648 m/s
7500 m/s
Olympic sprinter
UK motorway
Earth satellite
500 m/s
Can you match the correct speeds
m/s
340 m/s
Walking speed
Light speed
Concorde
1.7 m/s
31 m/s
833 m/s

8. Average speed ( m/s ) Light speed 300000000 m/s Earth in orbit
Earth satellite
7500 m/s
Fast jet
833 m/s
Concorde
648 m/s
Air molecule
500 m/s
Sound
340 m/s
747 jumbo jet
270 m/s
Falcon
97 m/s
High speed train
60 m/s
UK motorway
31 m/s
UK town
13.4 m/s
Familiarisation with realistic speeds in m/s to aid calculations.
Olympic sprinter
10.3 m/s
Walking speed
1.7 m/s
Snail
0.006 m/s

9. What is speed? When we talk about speed we mean…
the distance covered by an object in a
given time.

10. What is speed? If Hamish (the dog) runs 10 metres in 2
seconds, what is his speed?

11. What is speed?
His speed is 5 metres per second.
So speed is

12. What is speed?
If you forget the formula think of cars travelling at 30 kilometres per hour km
Per
Hour =

13. Key words: average speed
By the end of this section you will be able to:
Describe how to measure an average speed
Carry out calculations involving distance, time
and average speed.

14. distance
speed
time

15. Speed Calculations
A cyclist travels 100 m in
12 s. What is her speed?

16. Step 1: write down what you know.
d = 100 m t = 12 s speed = ?

17. Step 2: write down your formula. You can use the triangle to help you but remember you get no marks for this!
d = 100 m t = 12 s speed = ?
d = speed x t

18. d = speed x t Step 3: substitute in your values. d = 100 m t = 12 s

19. d = speed x t 100 = speed x 12 Step 4: rearrange d = 100 m t = 12 s

20. d = speed x t 100 = speed x 12 speed = = 8.33 100 12 Step 5: calculate
d = 100 m
t = 12 s
speed = ?
100 12

21. d = speed x t 100 = speed x 12 Speed = = 8.33 m/s 100 12
Step 6: units!!!!
d = speed x t
100 = speed x 12
Speed = = 8.33 m/s
d = 100 m
t = 12 s
speed = ?
100 12

22. Key words: average speed, instantaneous
By the end of this section you will be able to:
Describe how to measure instantaneous speed.
Identify situations where average speed and
instantaneous speed are different.

23. Instantaneous and average speed
Are instantaneous and average speed the same?

24. Instantaneous or average?
A car’s speed between North Berwick and
Edinburgh
Average

25. Instantaneous or average?
The speed read from a car’s speedometer
Instantaneous

26. Instantaneous or average?
A tennis ball’s speed as it crosses the net
Instantaneous

27. Instantaneous or average?
A racing car’s speed over a lap of the track
Average

28. Instantaneous or average?
A parachutist’s speed as he/she lands
Instantaneous

29. Scalars and Vectors Imagine a boat making a distress call to the
coastguard.
The boat tells the
coastguard he is 60 km
from Aberdeen.

30. Scalars and Vectors Is this enough information for the
coastguard to find
the boat?

31. Scalars and Vectors

32. distance (size) direction Scalars and Vectors
The coastguard needs both
distance (size)
and
direction
to find the boat.

33. Scalars and Vectors - Definition
A scalar is a quantity which has only
magnitude (size). It is defined by a
number and a unit.
A vector is a quantity which has
magnitude (size) and direction. It is
defined by a number, a unit and a
direction.
Print for lab books

34. Distance and Displacement
A pupil walks from her house to her school.
Her brother makes the same journey, but via a shop.
How far has the girl walked?
How far has her brother walked?
500 m
300 m
400 m

35. Distance and Displacement
The girl has walked 500 m.
Her brother has walked 700 m.
Distance is a scalar quantity – it can be defined simply by a number and unit.
500 m
300 m
400 m

36. Distance and Displacement
Distance is simply a measure of how much ground an object has covered.
500 m
300 m
400 m

37. Distance and Displacement
But how far out of place is the girl? And her brother?
Displacement is a vector which requires number, unit and direction.
500 m
300 m
400 m

38. Distance and Displacement
The girl has a displacement of 500 m at a bearing of 117° East of North.
500 m
300 m
400 m

39. Distance and Displacement
What is her brother’s displacement?
500 m
300 m
400 m

40. Distance and Displacement
Her brother has a displacement of 500 m at a bearing of 117° (117° East of North).
500 m
300 m
400 m

41. Distance and Displacement
Their displacement (how far out of place they each are) is the same.
500 m
300 m
400 m

42. Speed and Velocity
Speed is a scalar quantity requiring only magnitude (number and unit).
Velocity is a vector, requiring magnitude and direction.
Print for lab books

43. Speed and Velocity Speed tells us how fast an object is moving.
Velocity tells us the rate at which an object changes position.
Print for lab books
Physics animations?

44. Speed and Velocity Imagine a person stepping one step
forward, then one step back at a speed of
0.5 ms-1.
What is the person’s velocity? Remember
velocity keeps track of direction. The
direction of the velocity is the same as
the direction of displacement.

45. Speed and Velocity
Print for lab books

46. Key words: vectors, scalars, distance, displacement, speed, velocity.
By the end of this section you will be able to:
Describe what is meant by vector and scalar quantities
State the difference between distance and
displacement
State the difference between speed and velocity
State that force is a vector quantity
Use a scale diagram to find the magnitude and direction
of the resultant of two forces acting at right angles to
each other.
Wednesday 29th August

47. Distance and Displacement

48. Speed and Velocity

49. A physics teacher walks 4 meters East, 2 meters South, 4 meters West, and finally 2 meters North. The entire motion lasted for 24 seconds. Determine the average speed and the average velocity.
                                                         

50. The physics teacher walked a distance of 12 meters in 24
                                                         
The physics teacher walked a distance of 12 meters in 24
seconds; thus, her average speed was 0.50 m/s.
However, since her displacement is 0 meters, her average
velocity is 0 m/s. Remember that the displacement refers to
the change in position and the velocity is based upon this
position change. In this case of the teacher's motion, there is
a position change of 0 meters and thus an average velocity of
0 m/s.

51. Scalar or Vector?

52. Key words: vectors, scalars, resultant, scale diagram
By the end of this lesson you will be able to:
Describe what is meant by vector and scalar quantities
State the difference between distance and
displacement
State the difference between speed and velocity
State that force is a vector quantity
Use a scale diagram to find the magnitude and direction
of the resultant of two forces acting at right angles to
each other.
Thursday 30th August.

53. Vectors Vectors can be represented by a line
drawn in a particular direction.
The length of the line represents the
magnitude of the vector.
The direction of the line represents the
direction of the vector.

54. Addition of Vectors When two or more scalars are added
together, the result is simply a numerical
sum.
For example a mass of 3kg and a mass of
5 kg, when added, make a mass of 8kg.

55. Addition of Vectors 8 N When two or more vectors are added
together, providing they act in the same
direction, the addition is straightforward.
5 N
3 N
8 N

56. Addition of Vectors 2 N If they are acting in opposite directions 5 N

57. Key words: vectors, resultant
By the end of this section you will be able
to:
Use Pythagoras and Trigonometry to find
the magnitude and direction of the
resultant of two forces acting at right
angles to each other.
Thursday 30th August

58. Addition of Vectors The resultant of two or more vectors
which act at angle to each other can be
found either using a scale diagram, or by
Pythagoras and trigonometry.

59. To find the resultant of a set of vectors using a scale diagram
1. Decide on a suitable scale and write this
down at the start
2 Take the direction to the top of the page as
North. Draw a small compass to show this.
3 Draw the first vector ensuring it is the
correct length to represent the magnitude
of the vector, and it is the correct
direction.

60. To find the resultant of a set of vectors using a scale diagram
Draw an arrow to represent the second
vector starting at the head of the first.
Vectors are always added head to tail.
5 The resultant vector can now be determined
by drawing it on the diagram from the tail
of the first to the head of the last vector.
The magnitude and direction of this vector
is the required answer.
6 The final answer must have magnitude and direction – either a bearing from North or an angle marked clearly on the diagram

61. Scale Diagrams
Scale: remember if the question is in ms-1 then your scale should be a conversion from cm to ms-1.
Direction: draw compass on page
1st vector: length and direction
2nd vector: tail of 2nd starts at tip of first
Resultant vector: tail of 1st to tip of last
Answer must include magnitude (including units) and direction
Print for lab books

62. Scale Diagrams Direction should be given as a three
figure bearing from North
e.g. 045° or 175° or 035°
If you give any other angle, you must
clearly mark it on the scale diagram.
Print for lab books

63. A car travels 100 km South, then 140 km
East. The time taken for the whole
journey is 3 hours.
Using a scale diagram (and the six step
process) find
the car’s total distance travelled
its average speed
its overall displacement
its average velocity
Review on board – pupils to come up and draw / write

64. Scale Diagrams Scale diagrams are used to find the
magnitude and direction of the resultant
of a number of a set of vectors.

65. The tropical island of
Sohcahtoa

66. The tropical island of
Sohcahtoa

67. The tropical island of
Sohcahtoa

68. The tropical island of
Sohcahtoa
Print for lab books

69. hyp
opp θ°
adj
Print for lab books

70. Tan = Opp/Adj; Cos= Adj/Hyp;
The Old Arab Carried A
Heavy Sack Of Hay
Tan = Opp/Adj; Cos= Adj/Hyp;
Sin=Opp/Hyp

71. hyp
opp θ°
adj

72. N
+ 3 km North E
4 km East
Remember: The vectors above are not tip to tail. You must join them tip to tail

73. N
R = ?
+ 3 km North  E
4 km East
= Bearing of

74. We ADD vectors HEAD to TAIL [tip to toe]6N
6N North, 8N East - what is the resultant force R ?
We ADD vectors HEAD to TAIL [tip to toe] 8N 6N R  8N

75. Key words: acceleration, velocity
By the end of this section you will be able to:
Explain the term “acceleration”
State that acceleration is the change in
velocity per unit time
Carry out calculations involving the relationship
between initial velocity, final velocity, time and
uniform acceleration.

76. Measuring Acceleration Activity
What do you expect to happen to the value of acceleration as the light gate is moved further up the slope?
Position of light gate from bottom of slope
Acceleration (m/s2)
1st attempt
2nd attempt
3rd attempt
Position 1 m
Position 2
Position 3
Position 4
Average acceleration (m/s2)
Print for lab books

77. What is acceleration?
Acceleration is the change in velocity of an object per second (in one second).
Is acceleration a vector or scalar quantity?

78. Acceleration What is the definition of acceleration?
Is it a vector or a scalar?
Acceleration is the rate of change of velocity per unit time OR change in velocity per unit time.
Vector – since velocity is a vector.

79. What is acceleration? The rocket starts off at 0 m/s and 1
second later is travelling at 10 m/s.
What is its acceleration?
10 metres per second per second
10 m/s2
change in speed
in one second

80. Calculating acceleration
We need to know…
the change in velocity so…
initial velocity (u)
final velocity (v)
and…
time (t)

82. change in velocity
in one second

83. Acceleration a = acceleration measured in m/s2
u = initial velocity measured in m/s
v = final velocity measured in m/s
t = time measured in s

84. Units of acceleration a = acceleration is measured in m/s2
final velocity – initial velocity
a =
time
acceleration is measured in m/s2
If the speed is measured in kilometres per hour, acceleration can be measured in
kilometres per hour per second.

85. Acceleration An object accelerates at a rate of 4 m/s2.
What does this mean?
The object goes 4 m/s faster each
second.

86. Acceleration The object goes 4 m/s faster each second.
If the object is initially at rest, what
is its velocity after:
1s? 4 m/s
2s? 8 m/s
3s? 12 m/s
4s? 16 m/s

87. Acceleration What does it mean if an object has a negative
value of acceleration?
It means that it is slowing down.
For example: an object which has an
acceleration of -2 m/s2 is becoming 2 m/s
slower each second.

88. Acceleration Calculations
A car, starting from rest, reaches a
velocity of 18 m/s in 4 seconds. Find the
acceleration of the car.
What do I know?
Initial velocity u = 0 m/s
Final velocity v = 18 m/s
time t = 4 s

89. Acceleration Calculations
What do I know?
Initial velocity u = 0 m/s
Final velocity v = 18 m/s
time t = 4 s
Formula?
Example on p5 to do themselves

90. Acceleration Calculations
A cheetah starting from rest accelerates
uniformly and can reach a velocity of 24
m/s in 3 seconds. What is the
acceleration?
Use technique and show all working!
Units!!

91. Acceleration Calculations
A student on a scooter is travelling at
6 m/s. 4 seconds later, she is travelling at
2 m/s. Calculate her acceleration.
Use technique and show all working!
Units!!
What do you notice about her change in
velocity?

92. Rearranging the acceleration equation
v-u
a t
Pupils found rearranging the equation difficult!

93. Rearranging the acceleration equation
v-u
a t

94. Key words: acceleration, velocity
By the end of this section you will be able to:
Explain the term “acceleration”
State that acceleration is the change in
velocity per unit time
Carry out calculations involving the relationship
between initial velocity, final velocity, time and
uniform acceleration.
Graph results

95. Acceleration using two light gates
The length of the mask is 5 cm. Calculate
the acceleration.
Remember calculate u (initial velocity) and
v (final velocity) and use

96. Acceleration using a double mask
The length of each section mask is 4 cm. The gap is also 4 cm. Calculate the acceleration.
Remember calculate u (initial velocity) and
v (final velocity) and use

97. Key words: acceleration, velocity, displacement
By the end of this seection you will be able to:
Draw velocity-time graphs of more than one
constant motion.
Describe the motions represented by a
velocity-time graph.
Calculate displacement and acceleration, from
velocity-time graphs, for more than one constant
acceleration.
Tuesday 11th September

98. Graphing Motion Information about the motion of an
object can be obtained from velocity-time
graphs.
Similarly, we can graph motion based on
descriptions of the motion of an object.

99. Velocity-time graph The motion of a moving object can be
represented on a velocity – time graph.
Virtual Int 2 Physics – can pupils predict – remember area under speed time graph = distance, so area under velocity time graph = displacement.

100. Vectors and Direction direction.
When dealing with vector quantities we
must have both magnitude and
direction.
When dealing with one-dimensional
kinematics (motion in straight lines) we
use + and – to indicate travel in opposite
directions. We use + to indicate acceleration
and – to indicate deceleration.

101. Velocity-Time Graphs Describe the motion of this object.
Constant velocity – does not change with time

102. Velocity-Time Graphs Describe the motion of this object.
Increasing with time – constant acceleration

103. Velocity-Time Graphs Describe the motion of this object.
Decreases with time – constant deceleration

104. Velocity-Time Graphs
Describe the motion of this object.

105. Speed-Time Graphs Calculate the distance covered by the object
in the first 10 s of its journey.
The area under the graph tells us the distance
travelled.

106. Speed-Time Graphs Calculate the distance covered by the object
in the first 10 s of its journey.
The area under the graph tells us the distance
travelled.

107. Describe the effects of forces in terms of their ability to
Key words: forces, newton balance, weight, mass, gravitational field strength.
By the end of this section you will be able to:
Describe the effects of forces in terms of their ability to
change the shape, speed and direction of travel of an object.
Describe the use of a newton balance to measure force.
State that weight is a force and is the Earth’s pull on an
object.
Distinguish between mass and weight.
State that weight per unit mass is called the gravitational
field strength.
Carry out calculations involving the relationship between weight, mass and
gravitational field strength including situations where g is not equal to 10
N/kg.

108. What effect can a force have?
Force is simply a push or a pull.
Some forces (e.g. magnetic repulsion, or
attraction of electrically charged
objects) act at a distance.

109. What is force? A force can change the shape of an object
change the velocity of an object
change the direction of travel of an object

110. Units of Force?
Force (F) is
measured in
newtons (N).

111. Measuring Forces A Newton (or spring) balance can be used to measure
Show newton balances – hang masses on and read off force.

112. Mass and Weight We often use the words mass and weight
as though they mean the same…
but do they?

113. Mass and Weight An object’s mass is
a measure of how much “stuff” makes up
that object – how much matter, or how
many particles are in it.
Mass is measured in
grams or kilograms.

114. Mass and Weight An object’s weight is
the force exerted by gravity on a mass.
Since it is a force, weight must be
measured in
newtons.

115. Investigating the relationship between mass and weight
How can we find the relationship between
mass and weight?
A newton balance can be used to find the
weight of known masses.

116. Results
Mass
Weight in N
100g
200g
300g
400g
500g
1kg
2kg
5kg

117. Relationship between mass and weight
From this we can see a relationship
between mass and weight
100g = 0.1 kg -> 1 N
1kg -> 10 N
To convert kg -> N multiply by 10
To convert N -> kg divide by 10

118. Gravitational Field Strength (g)
Gravitational field strength on Earth is
10 N / kg

119. What is gravitational field strength?
This is the pull of gravity on each
kilogram of mass.
So on Earth, the pull of gravity on a 1kg
mass is
10 N

120. What is gravitational field strength?
and the pull of gravity on a 2 kg mass is
20 N

121. A planet’s gravitational field strength is the pull of gravity on
Definition
A planet’s gravitational
field strength is the
pull of gravity on
a 1 kg mass.

122. Gravity in the universe
Is gravitational field strength always the
same?
No! It varies on different planets.

123. Your weight on different planets
Use the website to find your weight on
different planets for a mass of 60 kg (a
weight of 600 N on Earth).
From this calculate the gravitational field
strength for each planet.

124. Mass on Earth = 60 kg
Weight on Earth = 600 N
Gravitational field strength =
Weight on Mercury = N g =
Weight on Venus = N g =
Weight on the Moon = 99.6 N g =
Weight on Mars = N g =
Weight on Jupiter = N g =
Weight on Saturn = N g =

125. 10 N / kg Units for g We found g by dividing weight in newtons
by mass in kilograms.
What are the units for g?
10 N / kg

126. Which of the planets has the greatest
gravitational field strength?
Why do you think this is the case?

127. Weight, mass and gravity
We have seen that there is a link between
weight, mass and gravity.
On Earth
1 kg acted on by 10 N / kg weighs 10 N
m x g = W
mass
Gravitational field strength g
weight

128. Weight, mass and gravity
W = mg
Why is weight measured in newtons?
Gravitational field strength measured in N / kg
Mass measured in kg
Weight measured in newtons

129. Key words: friction, force
By the end of this section you will be able to:
State that the force of friction can oppose
the motion of an object.
Describe and explain situations in which
attempts are made to increase or decrease
the force of friction.
18th September 2007

130. Frictional Forces Moving vehicles such as cars can slow
down due to forces acting on them.
These forces can be due to…
road surface and the tyres
the brakes
air resistance.

131. Frictional Forces The force which tries to oppose motion is
called the force of friction.
A frictional force always acts to slow an
object down.

132. Increasing Friction In some cases, we want to increase
friction. Some examples of this are:
Car brakes – we need friction between
the brake shoes and the drum to slow
the car down
Bicycle tyres – we need friction to give
“grip” on the surface

133. Increasing Friction On the approach to traffic lights and
roundabouts, different road surfaces are
used to increase friction compared with
normal roads.

134. Decreasing Friction In some cases, we want to decrease
friction. Some examples of this are:
Ice skating
Skiing
Aircraft design

135. Reducing Friction Friction can be reduced by:
Lubricating the surfaces – this generally
means using oil between two metal
surfaces. This is done in car engines to
reduce wear on the engine – metal parts
aren’t in contact because of a thin layer
of oil between them.

136. Reducing Friction Friction can be reduced by:
Separating surfaces with air (e.g. a
hovercraft).
Making surfaces roll (e.g. by using ball
bearings).

137. Reducing Friction Friction can be reduced by:
Streamlining. Modern cars are designed
to offer as little resistance (or drag) to
the air as possible, reducing friction on
the car.

138. Streamlining
Cars, aeroplanes and rockets are streamlined (that is, have their
drag coefficient reduced) by:
Reducing the front area
Having a smooth body shape

139. Key words: force, vector, balanced forces
By the end of this section you will be able
to:
State that force is a vector quantity.
State that forces which are equal in size but
act in opposite directions on an object are
called balanced forces and are equivalent to
no force at all.
Explain the movement of objects in terms of
Newton’s first law.

140. Force and direction. Force is a vector quantity. What do we
mean by this?
To describe it fully we must have size
and direction.

141. Balanced Forces F F
Balanced forces are EQUAL FORCES which act in OPPOSITE DIRECTIONS. They CANCEL EACH OTHER OUT.

142. If balanced forces act on a STATIONARY OBJECT, it REMAINS STATIONARY.
If balanced forces act on a MOVING OBJECT, it continues moving in the same direction with CONSTANT VELOCITY. F

143. This is summarised by NEWTON’S FIRST LAW which states:
An object remains at rest, or moves in a straight line with constant velocity unless an UNBALANCED FORCE acts on it.

144. To understand NEWTON’S FIRST LAW remember:
An object tends to want to keep doing what it is doing (so if it is sitting still it wants to stay that way, and if it is moving with constant velocity it wants to keep going).

145. This reluctance to change motion is known as inertia.
The greater the mass, the greater the reluctance.
Think! Is it easier to stop a tennis ball travelling towards you at 10 m/s or to stop a car travelling towards you at 10 m/s?

146. Forces and Supported Bodies
A stationary mass m
hangs from a rope.
What is the weight of
the mass? In what
direction does
this act?
W = mg downwards m

147. Forces and Supported Bodies
The mass is stationary.
Newton’s law tells us
that the forces must be
balanced forces.
The weight is
counterbalanced by a
force of the same size
acting upwards due to
the tension in the
string. m

148. Forces and Supported Bodies
A book of mass m
rests on a shelf.
What is the weight of
the book? In what
direction does
this act?
W = mg downwards m

149. Forces and Supported Bodies
The mass is stationary.
Newton’s law tells us
that the forces must be
balanced forces.
The weight is
counterbalanced by a
force of the same size
acting upwards due to
the shelf. m

150. What forces are acting on this stationary hovering helicopter?
lift =
W = mg
W = mg

151. Newton’s First Law Newton’s first law tells us that when the
forces on an object are balanced, a
stationary object will remain stationary.
But it also says that if when forces are
balanced, an object moving at constant
velocity will continue in the same direction
with the same velocity.

152. The ENGINE FORCE and the FRICTION FORCE must be equal.
A moving car
If a car moves with constant velocity, then what forces are acting on it?
The ENGINE FORCE and the FRICTION FORCE must be equal.
Engine force
Friction force

153. Newton’s Law & Car Seat Belts
If a car stops suddenly, someone inside the car appears to be “thrown forwards”.
In fact, they simply carry on moving with the car’s previous speed.
A seat belt prevents this happening by applying an unbalanced force to the person, in the direction opposite to motion. This causes rapid deceleration.

154. No seatbelt – what’s going to happen when the car hits the wall?
Explain this in terms of Newton’s 1st law.

155. What’s going to happen when the motorbike hits the wall?
Explain this in terms of Newton’s 1st law.

156. Air bags
Air bags produce a similar effect to seatbelts. They apply a force which opposes the motion, causing rapid deceleration.
The large surface area also spreads the force of impact, reducing the pressure and reducing injury.

157. Forces in a Fluid Terminal velocity
Any free-falling object in a fluid (liquid or gas) reaches a top speed, called ‘terminal velocity’.

158. Terminal Velocity
The air resistance acting on a moving object increases as it gets faster.
Terminal velocity is reached when the air-resistance (acting upwards) has increased to the same size as the person’s weight (acting downwards)

159. a = -10 m/s2 time = 0s, velocity = 0 m/s, friction = 0 N
Friction Ff(air resistance) = 0 N
a = -10 m/s2
W = weight

160. Ff
a < -10 m/s2 v
W = weight

161. Equal & opposite forces Acceleration zero Terminal velocityFf
a = 0 m/s2 v
W = weight

162. Velocity – Time Graph
velocity
(m/s)
Terminal velocity
time (s)

163. air resistance
Terminal velocity is reached when the air resistance balances the weight.
weight

164. Terminal Velocity What effect does opening a parachute
have on the terminal velocity?
When the parachute is opened, air resistance
increases a lot. There is now an unbalanced force
upwards, which causes deceleration. The velocity
decreases, and the air resistance decreases until
the forces are balanced again. The parachutist
falls to the ground with a lower terminal velocity.

165. Key words: Newton’s second law, unbalanced forces, mass, force,
acceleration
By the end of this section you will be able to:
Describe the qualitative effects of the change of
mass or of force on the acceleration of an object
Define the newton
Carry out calculations using the relationship
between a, F and m and involving more than
one force but in one dimension only

166. The example of the parachutist accelerating until the forces are balanced helps us to understand NEWTON’S SECOND LAW which states:
When an object is acted on by a constant UNBALANCED FORCE the body moves with constant acceleration in the direction of the unbalanced force.

167. Force, mass and acceleration
Acceleration (m/s2)
F = ma
Force (N)
mass (kg)

168. Force, mass and acceleration
One newton (1N) is the force required to
accelerate 1 kg at 1 m/s2

169. F = ma
Find the unbalanced force required to accelerate a 4 kg mass at 5 m/s2
What do I know?
m = 4kg
a = 5m/s2
F = ma
F= 4 x 5
F = 20 N

170. Key words: free body diagrams, resultant force
By the end of this section you will be able
to:
Use free body diagrams to analyse the forces
on an object
State what is meant by the resultant of a
number of forces
Use a scale diagram, or otherwise, to find the
magnitude and direction of the resultant of
two forces acting at right angles to each
other.

171. Newton’s First Law A body remains at rest, or continues at
constant velocity, unless acted upon by an
external unbalanced force.
(that is objects have a tendency to keep
doing what they are doing)

172. Newton’s Second Law Newton’s Second Law is about the
behaviour of objects when forces are not
balanced.
The acceleration produced in a body is
directly proportional to the unbalanced
force applied and inversely proportional to
the mass of the body.

173. Newton’s Second Law In practice this means that
the acceleration produced increases as
the unbalanced force increases
the acceleration decreases as the mass of
the body increases

174. Which forces? An object may be acted upon by a number of forces but
only an overall unbalanced force
will lead to acceleration in the direction
of that force.

175. Forces are measured in…?
Newton’s Second Law can be written as
or more commonly

176. Forces are measured in…?
which gives us the definition of the Newton:
1N is the resultant (or unbalanced)
force which causes a mass of 1kg to
accelerate at 1m/ s2

177. Quick Quiz 5 10 5 10 1 Unbalanced force (N) Mass (kg) Acceleration
(m/ s2) 10 2 20 4 5 5 10 5 10 1

178. Direction of force To the right To the right
Consider the oil drop trail left by the car
in motion.
In which direction is the acceleration?
In which direction is the unbalanced
force?
To the right
To the right

179. Direction of force Consider the oil drop trail left by the car
in motion.
In which direction is the unbalanced
force?
To the left – the car is moving to the right and slowing down.

180. Newton’s First and Second Laws
Remember
Forces do not cause motion
Forces cause acceleration

181. Free-Body Diagrams Free body diagrams are special
examples of a vector diagram.
They show the relative magnitude
and direction of all forces acting
on an object.
They are used to help you identify
the magnitude and direction of an
unbalanced Force acting on an
object.
Weight

182. Using Newton’s Second Law
In the simplest case m
Fun

183. Using Newton’s Second Law
Direction of acceleration?
Direction of unbalanced force?
Formula for calculating acceleration? m F1 F2 Fu

184. Solving Problems Always draw a diagram showing all known
quantities (forces – magnitude and
direction, resultant acceleration and
direction, mass of object(s) )
Remember that Fun=ma can be applied to
the whole system
When working in the vertical direction
always include the weight

185. Key words: acceleration, gravitational field strength, projectiles
By the end of this section you will be able
to:
Explain the equivalence of acceleration due to
gravity and gravitational field strength
Explain the curved path of a projectile in
terms of the force of gravity
Explain how projectile motion can be treated
as two separate motions
Solve numerical problems using the above method
for an object projected horizontally.

186. Acceleration due to Gravity
Definition:
A planet’s gravitational field strength equals the force of gravity PER UNIT MASS.
Units?
N/kg
To calculate an object’s weight, use this equation -

187. Acceleration due to Gravity
Near a planet’s surface all objects experience the same gravitational acceleration.
This acceleration is numerically equal to the planet’s gravitational field strength.

188. Acceleration due to Gravity
For example, on Earth –
g = 10 N/kg
A free-falling object will experience acceleration of a = -10 m/ s2
What does the –ve sign tell you?

189. Gravitational field strength
Is the gravitational field strength the same on each
planet?
How does distance affect gravitational field strength?
It decreases the further away you are from the planet’s
surface.
What will happen to the weight of an object as it gets
further from the surface? Explain your answer.
It will decrease.

190. The force of gravity near
the Earth’s surface gives
all objects the same
acceleration.
So why doesn’t the
feather reach the ground
at the same time as the
elephant?

191. Why are the gaps
between the balls
increasing?

192. An object is released from rest close to the Earth’s
surface. Which formula can be used to find its velocity
at a given time?
v = u + at
where v = ? u = a = t =
What is its velocity:
At the time of release?
After 1 second?
After 2 seconds?
After 3 seconds?
After 4 seconds?

193. Projectiles

194. Forces acting on projectiles
What would happen to a ball kicked off a
cliff, in the absence of gravity?

195. Forces acting on projectiles
There would be no vertical motion
therefore the ball would continue at
constant speed in a straight
line (remember Newton’s first law)

196. Objects projected horizontally Think about…
What is the initial vertical speed of a
projectile fired horizontally?
How will the horizontal speed vary during
the object’s flight?
0 m/s
It will remain the same as the initial horizontal speed.

197. Objects projected horizontally Think about…
Describe the vertical motion of an object
projected horizontally:
It will accelerate downwards due to gravity.

198. Objects projected horizontally Think about…
What formula can be used to find the
horizontal displacement of an object
fired horizontally if horizontal velocity
and time of flight are known?
time of flight (s)
horizontal displacement (m)
sh = vht
horizontal velocity (m/s)

199. Which ball will hit the ground first?

200. Summary Horizontal motion Vertical motion Forces Are there forces
present? If so, in
what direction are
they acting? No
Yes
The force of gravity
acts downward
Acceleration
Is there acceleration?
If so, in what
direction? What is
the value of the
acceleration?
Acceleration = "g" downward
at 10 m/s2
Velocity
Constant or changing?
Constant
Changing
by 10 m/s each second

201. Solving Numerical Problems
Always write down what you know – many questions have a lot of text surrounding the Physics so pick out the information from the question
Write down other relevant information you have e.g. acceleration due to gravity
Select formula – this isn’t a test of memory so while you should learn your formulae, don’t be afraid to check against the data book or text book
Substitute values and rearrange formula
Write answer clearly remembering magnitude and direction, and units.

202. Example A flare is fired horizontally out to sea from a
cliff top, at a horizontal speed of 40 m/s. The
flare takes 4 s to reach the sea.
What is the horizontal speed of the flare after 4 s?
There are no forces acting in the horizontal. The
horizontal speed remains the same = 40 m/s.

203. Example (b) Calculate the vertical speed of the flare after 4s
final speed v = ?
initial vertical speed u = 0 m/s Initial vertical speed is always 0 m/s!
acceleration a = 10 m/s2
time t = 4 s
v = u + at
v = x 4
v = 40 m/s

204. Example (c) Draw a graph to show how vertical speed varies with time.
Initial vertical speed = 0 m/s
Final vertical speed = 40 m/s

205. Example (d) Use this graph to calculate the height of the cliff.
Displacement = area under velocity-time graph
½ bh = ½ x 4 x 40
= 80 m
Height of cliff = 80 m

206. Key words: Newton’s third law, newton pairs
By the end of this section you will be able to:
State Newton’s third law
Identify “Newton pairs” in situations involving
several forces
State that momentum is the product of mass
and velocity.
State that momentum is a vector quantity.

207. Forces acting between objects
Newton realised that
When a body is acted upon by a force there must be another body which also has a force acting on it. The forces are equal in size but act in opposite directions.

208. Newton’s Third Law
If object A exerts a force on object B, then B exerts an equal and opposite force on A
Forces always occur in equal and opposite pairs
For every action there is an equal and opposite reaction

209. Firing a gun
Force of GUN on BULLET
Force of BULLET on GUN

210. Force of RUNNER on BLOCKS
Starting a sprint
Force of RUNNER on BLOCKS
Force of BLOCKS on RUNNER

211. A falling apple
Force of EARTH on APPLE
Force of APPLE on EARTH

212. A Rocket
Force of GAS on ROCKET
Force of ROCKET on GAS

213. Key words: work done, energy, force, distance, power, time
By the end of this section you will be able
to:
State that work done is a measure of the
energy transferred.
Carry out calculations involving the
relationship between work done, force and
distance.
relationship between work done, power and
time.

214. Work done? What is meant by work done in Physics?
When a force acts upon an object to
cause a displacement of the object, it is
said that work was done upon the object.

215. Work done? There are three key ingredients to work –
force, displacement, and cause.
In order for a force to qualify as having done
work on an object, there must be a
displacement and the force must cause the
displacement.
Note; at this level, we can use distance instead of displacement.

216. Work done? Formula linking work done, force and displacement?
Examples of work done?
a horse pulling a plough through the field
a shopper pushing a grocery cart down the aisle of a supermarket
a pupil lifting a backpack full of books upon her shoulder
a weightlifter lifting a barbell above his head
an Olympian launching the shot-put, etc.
In each case described here there is a force exerted upon an
object to cause that object to be displaced.

217. Work done A dog pulls a 4 kg sledge for a distance on
15 m using a force of 30 N. How much
work does he do?
What do I know?
F = 30N
d = 15m

218. Work done
What do I know?
F = 30N
d = 15m
Formula?

219. Power Power is the rate of doing work i.e. if
work is done then the work done per
second is the power.
Energy in joules
time in seconds
Power in watts (joules per seconds)

220. Power A dog pulls a 4 kg sledge for a distance on
15 m using a force of 30 N in 20 s.
Calculate the power of the dog.
What do I know?
F = 30N
d = 15m
t = 20s

221. Power
What do I know?
F = 30N
d = 15m
t = 20s
Formula?

222. Power
What do I know?
F = 30N
d = 15m
t = 20s
Ew = 450J
Formula?

223. By the end of this section you will be able to:
Key words: gravitational potential energy,
mass, gravitational field strength, kinetic
energy
By the end of this section you will be able
to:
Carry out calculations involving the relationship
between change in gravitational potential energy,
mass, gravitational field strength and change in
height.
between kinetic energy, mass and velocity.

224. Gravitational Potential Energy
…is the potential energy
gained by an object when
we do work to lift it
vertically in a gravitational
field.

225. Gravitational Potential Energy
The work done in lifting an
object vertically
What force is required?

226. Gravitational Potential Energy
To lift the object we must overcome the weight W=mg

227. Gravitational Potential Energy
Vertical distance – we call this height h

228. Gravitational Potential Energy

229. …is the energy associated with a moving object.
Kinetic Energy
…is the energy associated with a moving object.

230. Kinetic Energy
depends on…
The mass of the object

231. Kinetic Energy
depends on…
The velocity of the object

232. Kinetic Energy