1. Section 1 Describing Motion

2. Motion Motion is a change in position
Position depends on a reference frame
Frames of reference can be stationary or moving.

3. Frame of Reference
If you are sitting in a moving car, you are not moving if the car is the reference frame
But you are moving relative to someone standing on the curb

6. Measuring Motion Motion - A change of position
Speed -The distance an object travels per unit of time
Equation - speed = distance/ time (s = d / t)
SI units – meters per second (m/s)
Distance is usually measured in meters or kilometers
Time is usually measured in seconds or hours

7. Speed

8. Instantaneous Speed
Instantaneous speed of an object is the speed at a single instant in time
Example: At the moment this picture was taken the car was traveling 250 mph, that was it’s instantaneous speed at that exact moment

9. Constant and Average Speed
Constant speed
Speed that does not change
Example: The Earth rotates at a constant speed on it’s axis. (Once every 23 hours 56 minutes and 3seconds)
Average speed
Speed that does change
Average speed =
total distance (meters)
total time (seconds)

10. Velocity Velocity is speed with direction
Velocity is a vector that has size (speed) and direction
Objects have different velocities if they are moving at different speeds or if they are traveling in different directions

11. Objects have different velocities if they are moving in different directions

12. Velocity
Velocity of an object can change even if the speed remains constant
If the roller coasters speed stays constant its velocity will change because it is changing direction

13. Velocity Circular motion
In circular motion, the velocity is constantly changing.
This is because the direction is constantly changing

14. Graphing Motion
The motion of an object over a period of time can be shown on a distance-time graph
Time is plotted on the horizontal axis
Distance traveled is plotted on the vertical axis

15. Acceleration The rate at which velocity changes over a period of time
Equation
A = (Vf – Vo)/ T
A= acceleration
Vf = final velocity
Vo = original velocity
T = time
Units = m/s2
m = meters
s = seconds

16. Calculating Acceleration
I get into my car, start the engine and drive. After 5 seconds I am moving at 10 meters per second. What is my acceleration at this point in time?
Original velocity (Vo) =
0 m/s
Final velocity (Vf) =
10 m/s
Time = 5 seconds
10 m/s – 0 m/s = 10m/s
5s s
= 2 m/s2

17. Acceleration If acceleration is negative you are slowing down
If acceleration is positive you are speeding up

18. Result of rapid negative acceleration

19. Acceleration Acceleration can happen in two ways Changes in velocity
Changes in direction
Acceleration can be an increase or a decrease in velocity .

20. Speed-Time Graphs The vertical axis is the objects speed
The horizontal axis is the time
The line is pointing up, this indicates the rate of speed is increasing (positive)
The line is also curved, this indicates the rate of acceleration was uneven

21. Speed-Time Graphs
This graph indicates that acceleration increased at a constant rate
The speed then remained constant for a while
Then began to decrease
The speed became constant again
Then continued to decrease at a faster rate until it stopped

22. Forces
A force is a push or pull that one object exerts on another object
A force is also a vector that has size (strength) and direction

23. Forces The size of the force is the strength of it
The direction is which way the push or pull is applied
The SI unit used for force is the newton (N)
Force = Mass x Acceleration
N = 1kg x 1m/s2

24. Balanced Forces
When two or more forces act on an object they are combined to form the net force
When two or more forces act on an object and the net force is equal they are called balanced forces

25. Unbalanced Forces
When forces combine to produce a net force that is not zero the are unbalanced forces
The net force that caused the mule to be lifted up is the difference of the two forces (mule and cargo)

26. Unbalanced Forces Change Velocity
When forces acting on an object are balanced the velocity of the object does not change
When forces on an object are unbalanced the velocity of the object will change

27. Friction
Friction is the force that opposes the sliding motion of two surfaces that are in contact

28. What Causes Friction?
The size of the frictional force exerted depends on the material the surfaces are made from and the roughness of the surface
All surfaces have surfaces have bumps and dips, even highly polished ones

29. Static Friction
Static friction is the frictional force That prevents two surfaces in contact with each other from sliding past each other
Static friction is what is preventing this man from moving the truck

30. Sliding Friction
Sliding friction is the force that acts in the opposite direction to the motion of a surface sliding on another surface.
Sliding friction will a eventually cause the bear to come to a stop

31. Rolling Friction
Friction produced by objects such as wheels and ball bearings.
Tends to be less than sliding friction.

32. Air Resistance
Air resistance opposes the motion of objects that move through the air
Air resistance acts in the opposite direction to the object moving through it
The amount of air resistance depends on the speed, size and shape of the object

33. Terminal Velocity
After jumping from the aircraft the skydiver increases speed up to a steady maximum called terminal velocity.
The downward force of gravity (the Weight) is balanced by the upward force of air resistance (the Drag)

35. Momentum

36. Momentum – Mass of an object multiplied by its velocity
Equation –
P = mass x velocity
P = M x V
Units –
Kg m/s

38. Law of Conservation of Momentum
States that the total conservation of momentum of any group of objects remains the same unless outside forces act on the object.