1. Describing Motion
Chapter 9 Sec 1 & 2

2. Put into order the fastest animal to the slowest
Cat
Cheetah
Giant tortoise
Lion
Squirrel
Garden snail
Chicken
rabbit

3. Fastest – cheetah at 70 mph

4. Second fastest –lion @ 61 mph

5. 3 – Rabbit, 4 Cat

6. Human next!

7. 5 squirrel 6 chicken

8. Slowest – garden snail at 0.3 mph

9. Motion
Motion
Definition – an object is in motion if its distance from another other is changing.

10. How can you decide if you are moving?
Its relative! (relative is described as compared to a reference point)
Reference point
Motion

11. Reference Point – is an object used to compare if you are moving or not
For example if you are sitting in a moving car
If the moving car is the reference point, are not moving.
If the ground is the reference point you are moving.

12. Are you moving now?
What if your frame of reference is the Sun?

13. Speed versus Velocity

14. How can I determine speed???
How to calculate speed
If you know the distance an object travels in a certain amount of time then you can calculate the speed.
It is a rate!

15. Speed
Speed is the distance an object/person travels in a given amount of time.
Instantaneous speed – an object’s speed at a single instance of time (a car’s speedometer measures instantaneous speed)
Average speed – the distance traveled by an object/person divided by time.
Constant speed – an object’s speed is the same over time (does not change)

16. s d t Speed – rate of motion It is a scalar quantity!
It doesn’t matter which direction it is going in!

17. Applying Math
Suppose a cyclist travels 32 km for 2 hours and then travels 13 km for the next hour. What is the cyclist average speed?
Given
Work
Total distance =
Total time =
Avg speed = total d/ total time

18. t d v D. Calculations d = 100 m s = d ÷ t t = 20 s
Your neighbor skates at a speed of 4 m/s. You can skate 100 m in 20 s. Who skates faster?
GIVEN:
d = 100 m
t = 20 s
s = ?
WORK:
s = d ÷ t
s = (100 m) ÷ (20 s)
s = 5 m/s
You skate faster! v d t

19. How is speed different than velocity?

20. Velocity
Velocity is the object’s speed and its direction of its motion -

21. Speed vs. Velocity
A tornado is 1200m away and is moving at a speed of 200m/s. Should you be worried?
It depends on the storm’s direction and how long before it hits!

22. v Velocity It is a vector quantity. It includes direction!
A car has a velocity of 5 m/s north

23. How can this car be moving at the same speed but have different velocities?

24. Velocity When do objects have a different velocity?
Objects/persons have different velocity if they are moving at
Different speeds
And/or different directions

25. Graphing Motion