1. Motion And Forces``

2. Describing Motion

3. Motion Occurs when an object changes position relative to a reference point.

4. Distance
how far an object has traveled
Displacement
distance and direction of an objects change in position from starting point
Distance Vs. Displacement

5. Speed – the distance an object travels per unit time – rate of change
in position
Speed
Avg Speed (v) = total distance (d)/total time (t)
V = d/t

6. Type of Speed
Description
Example
INSRANTANEOUS
Speed at any given point in time
Driving a car and looking down at speedometer
AVERAGE
Total distance traveled divided by total time
Taking a road trip
CONSTANT
Speed that does not vary
Putting car in cruise control

7. Types of Speed
1. Constant Speed: speed stays the same
Ex.

8. 2. Average Speed: accounts for changes in speed over a certain distance
Example: On a road trip you drive 450 km and you drive through several cities with different speed limits, also you have to make several stops for gas and food so it takes you 5 hours. What is your average speed?

9. 3. Instantaneous Speed: speed at a single point in time
Ex. Radar gun

10. Steps to answer word problems:
Formula for Speed
Steps to answer word problems:
1. Write what you know and don’t know.
2. Write the formula.
3. Plug-n-Chug!
4. Write your answer.
5. Include the correct units
You must show ALL steps to get full credit for ANY math problem.

11. Practice Problem 1
If a cheetah runs 352 meters in 20 seconds, what is the speed of the cheetah?

12. Practice Problem 2
If a soccer ball is kicked down the field and it rolls at 17 m/s, how long will it take the soccer ball to roll 50 m?

13. Practice Problem 3
If a car is traveling at a speed of 68 km/h for 5 hours, how far has the car traveled?

14. Graphing Motion
The slope of a line on a distance – time graph gives the speed of an object in motion. Y
DISTANCE
Motion of an object can be plotted on a
distance – time
graph. X
TIME
X axis -> TIME
Y axis -> DISTANCE

15. Graphing Motion
Put the time on x-axis and the distance on y-axis

16. Motion Graphs
Time – Distance Graphs

17. Motion Graph # 1 Straight, Flat Line
As time , distance = 0
Distance (m)
Time (Sec)

18. Motion Graph # 2 Straight, Increasing Line
Distance (m)
As time , distance 
Time (Sec)

19. Motion Graph # 3 Straight, Decreasing Line
As time , distance 
Distance (m)
Time (Sec)

20. Motion Graph # 4 Changing Line
A changing line means changing distance
Distance increases  doesn’t change  distance decreases
Distance (m)
Time (Sec)

21. Motion Graph

22. Velocity the direction !
In order to completely describe the motion of an object we need to include not only the speed of the object, but also
the direction !

23. Speed vs Velocity Speed is how fast an object is moving
Ex: A storm moving at 75 km/hr
Velocity is how fast an object in moving in a certain direction
Ex. A storm moving at 75 km/hr towards the east

24. Race track Example
If the drivers go around the entire track at exactly 195 mph, is their speed constant? Is their velocity constant? Explain.

25. Equations for Speed and Velocity are the SAME
v=d/t

26. Practice Problem 1
If a westbound train has gone 359 miles in 5 hours, what is the velocity of the train?

27. Practice Problem 2
If a storm is traveling at 75 km/hr north and it will hit your town in 2 hours, how far away is the storm?

28. Acceleration

29. Velocity – includes speed of an object and the direction of its motion What is the difference between speed & velocity? Velocity includes direction where as speed does not.

30. Acceleration – rate of chance of velocity
Acceleration – rate of chance of velocity. Acceleration occurs when an object changes speed, its direction, or both.

31. Calculating Acceleration
Acceleration (meters/second²) = change in velocity (meters/sec) Time (seconds) * NOTE : Change in velocity = final velocity – initial velocity v= Vf - Vi Acceleration formula : a=Vf – Vi t
Calculating Acceleration

32. Positive Acceleration
A plane takes off…
a = Vf – Vi = 80m/s – Om/s
t s
a = 4m/s²
The plane is speeding up so acceleration is positive.

33. Negative Acceleration
A bike comes to a stop…
a = Vf – Vi = 0m/s – 3m/s
t s
a = -1.5m/s
The bike is slowing down so acceleration is negative.

34. Motion And Forces

35. Force — a push or pull applied to an object.

36. Net Force – When two or more forces act on an object at the same time
FORCES ARE =
BALANCED FORCES
NET FORCE = 0
FORCES
UNBALANCED
NET FORCE = +
COMBINED FORCES
NET FORCE = TWO FORCES ADDED TOGETHER

37. Friction – the force that opposes the sliding motion of two touching surfaces. Friction is caused by microscopic bumps on surfaces called microwelds.

38. TYPE OF FRICTION
DESCRIPTION
EXAMPLE
STATIC
Friction in which two surfaces are not moving past each other.
PUSHING A FRIDGE ACROSS A FLOOR
SLIDING
Friction where two surfaces slide past one another.
SLEDDING DOWN A HILL
ROLLING
Friction between a rolling object and surface it rolls on.
SKATEBOARD MOVING ON GROUND
FLUID
Friction when object moves through fluid, meaning either a liquid or gas
SKYDIVING
Air Resistance – friction – like force that opposes motion of objects that move through air – depends on speed, size & shape of object

39. Newton’s Laws Of Motion

40. Newton’s First Law of Motion
Also known as Law of Inertia!
An object in motion stays in motion, or an object at rest stays at rest until an unbalanced net force acts upon it.

41. Inertia – tendency of an object to resist any change in its motion.
WILL STAY AT REST UNTIL FORCE ACTS IN IT
GRAVITY
FRICTION
WILL CONTINUE IN MOTION UNTIL THESE FORCES ACT ON IT
WALL

42. Force = mass x acceleration
Newton’s Second Law of Motion A net force acting on an object causes the object to accelerate in the direction of the force. Acceleration is determined by size of force and the mass of an object.
(Kg * m/s²) (kg) (m/s²)
Force = mass x acceleration
F = m x a

43. Newton’s Third Law of Motion For every action (or force), there is an equal and opposite reaction (or force).
Momentum – property of moving object resulting from its mass and velocity.
ACTION REACTION
Momentum (p) = mass x velocity

44. Gravity

45. Gravity – any two masses that exert an attractive force on each other.
Gravity depends on mass & distance between objects
Weight – gravitational force exerted on an object; measured in units called Newtons
The greater the object mass, the stronger the gravitational force on it

46. A projectile follows a curved path and has:
Projectile Motion Projectile – anything that is thrown or shot through air
A projectile follows a curved path and has:
and V E R T I C A L
Motion perpendicular to Earth’s Surface
MOTION
Horizontal Motion
Motion parallel to Earth’s surface

47. Centripetal Force
Centripetal acceleration – acceleration toward the center of a curved or circular path
“centripetal” means toward the center
Centripetal force – force acting
toward the center of a curved
or circular path