1. Chapter 4
Linear Motion

2. 4.1 Motion is Relative
When we describe the motion of one object with respect to another, we say the object is moving relative to another.
An object is moving if its position relative to a fixed point is changing.
Chapter 10

3. 4.2 Speed
Speed is how fast an object is moving. The distance an object moves per unit of time. (Rate)
You can calculate the speed of an object by dividing the distance covered by time.
Speed = distance / time
Units
Chapter 10

4. 4.2 Speed The speed at any instant is called the instantaneous speed.
Average speed is the total distance covered divided by the time.
Average speed = total distance covered / time interval
Chapter 10

5. 4.3 Velocity Velocity is speed in a given direction.
Speed is a description of how fast an object moves; velocity is how fast and in what direction it moves.
Constant velocity means both constant speed and constant direction. If the speed and/or direction is changing, then the velocity is changing.
Chapter 10

6. 4.4 Acceleration
Acceleration is the rate at which velocity is changing.
You can calculate the acceleration of an object by dividing the change in velocity by time.
Acceleration = change of velocity / time interval
Chapter 10

7. 4.4 Acceleration What control do you use to accelerate your car?
Gas pedal – Speed up – Accelerate (+ acceleration)
Brake – Slow down - Decelerate (- acceleration)
Steering wheel – Change of direction. (centripetal acceleration)
Chapter 10

8. 4.4 Acceleration
Change in speed acceleration (along a straight line) = change in speed / Time interval
Chapter 10

9. 4.5 Free Fall
For each second of free fall, an object falls a greater distance than it did in the previous second.
v = at (a = Δv / Δ t) & v = gt
d = ½ at2 & d = ½ gt2
Chapter 10

10. 4.7 Graphs of Motion Speed versus time graph
For a freely falling object, the relationship is linear. They are directly proportional.
On a speed versus time graph the slope represents speed per time, or acceleration.
Chapter 10

11. 4.7 Graphs of Motion Distance versus time graph
For freely falling object, the relationship is quadratic and the curve is parabolic.
The slope of a line on a distance vs. time graph at any particular time equals the speed of the object at that time.
Chapter 10

12. 4.8 Air Resistance and Falling Objects
Air resistance noticeably slows the motion of things with large surface areas like falling feathers or pieces of paper. But air resistance less noticeably affects the motion of more compact objects like stones and baseballs.
Feather and Penny Demo
Chapter 10

13. How Fast, How Far, How Quickly How Fast Changes
Speed in free fall: v = gt
Distance in free fall: d = ½ gt2
Acceleration in free fall: a = g = 9.8 m/s2
Acceleration is the rate at which velocity changes - the rate of a rate.
Chapter 10

14. The Physics of Sport: Hang Time
d = ½ gt2
t(up or down) = square root (2d/g)
Chapter 10