1. Motion

2. Definition
Motion is a change in an object’s position relative to a reference point.

3. Motion is Relative
Relative – it is described compared to a REFERENCE POINT
Example: As a car drives away from school its position is changing relative to school.

4. Describing motion
We describe motion in words, with graphs and using mathematical quantities.
The mathematical quantities we use to describe motion are distance, time, speed, velocity and acceleration.

5. Describing motion These mathematical quantities have certain SI units.
Quantity
Unit
Distance
Meter
Time
Second
Speed/Velocity
Meter per Second
Acceleration
Meter per second squared

6. Speed: We are concerned with 3 different types of speed.
Speed is the rate of change in position.
We will talk about average speed, instantaneous speed, and constant speed.

7. Speed: Average Speed
Total distance traveled divided by the time interval during which the motion occurred.
s= d / t
t = d / s
d = s x t
Example: If you travel 200 miles
In 4 hours, your average speed is
50 mph.

8. Speed Instantaneous Speed
Speed at any instant
Example: In your trip,
you might be going
60 mph one moment and
Slowing down and stopping for a break a few moments later.

9. Speed Constant Speed Speed that does not change
Instantaneous speed that does not change
When an object has a constant speed, its average speed and instantaneous speed will be the same.

10. Velocity Speed AND direction
This is important for a full description of motion
Pilots need to know wind speed and direction.
Calculations of velocity are different than speed.
v= change in position / time

11. Velocity: Direction matters
Imagine that two birds leave the nest at the same time. The both fly at 10 km/h for 5 min, 12 km/h for 8 min, and 5 km/h for 10 min. Why don’t they end up at the same place?

12. A swimmer swims 50 m in 40 s. What is the swimmer’s average speed?
Problem
A swimmer swims 50 m in 40 s. What is the swimmer’s average speed?

13. A swimmer swims 20 m in 40 s. What is the swimmer’s average speed?
S = D/T
S = 50m/40s
S = 1.25m/s

14. Problem
What is the average speed (mph) for a car journey of 120 miles that began at 09:30am and finished at 12:00 noon?

15. Problem
What is the average speed (mph) for a car journey of 120 miles that began at 09:30 and finished at 12:00 noon?
S = D/T
D = 120
T = 2.5 hours (from 9:30 – 12:00)
S = 120m / 2.5h
S = 48 mph

16. How far does a bicycle travel at a speed of 6 m/s for 15 seconds?

17. How far does a bicycle travel at a speed of 6 m/s for 15 seconds?
s=d/t
6m/s = d/15s
15s (6m/s) = d/15s (15s)
90 m = d