1. Calculating Speed from a Distance-Time Graph
Average Speed = Distance Moved / Time taken
Calculate the average speed for each of the section

2. Speed is a vector quantity. It only has a size. It has no direction
Difference between Speed and Velocity
Speed is a vector quantity. It only has a size. It has no direction
For example 5 m/s or 100m/s
Velocity has direction and magnitude.
For example a velocity of 5m/s due North
or 30 m/s due East
Velocity can be negative or positive.
The sign of the velocity will indicate the direction of the velocity

3. Representing Velocity
Positive direction
5 m/s
This car is travelling at a velocity of 5m/s due West
This car is travelling at 2 m/s due South
OK....they have no drivers...

4. Representing Velocity
Velocity is represented by a VECTOR ARROW
The direction of the arrow shows the direction of the velocity
The length of the arrow represents the size of the velocity
Now try this:
Draw the velocity vectors for the following:
(a) A train travelling at 50 m/s due East
(b) A car travelling at 10 m/s due South
(c) A marathon runner at 2 m/s due West.

5. Velocity-time graphs A change in velocity is an acceleration
Acceleration can be positive or negative (deceleration)
Describe the acceleration in each of the sections 1 - 6

6. Calculating acceleration from a velocity-time graph
Acceleration = (Change in velocity) / Time taken
First Section:
a = (20 - 0) / 2 = 20/2 = 10 m/s each second
= 10 m/s2
Now calculate the acceleration in the other sections

7. Calculating distance moved from a velocity-time graph
The AREA under a velocity-time graph
is equal to the distance moved.
Divide the area under the graph
into rectangles and triangles
Calculate the area under each section
to obtain the distance moved for that section.
Area of triangle = 1/2 x base x height
Area of rectangle = length x width

8. Calculating distance moved from a velocity-time graph
Distance moved for Section 1
= 1/2 x base x height = 1/2 x 2 x20
= 20 m
Distance moved for Section 2
= width x height = 2 x 20 = 40 m

9. Investigation: How does the speed of a marble vary with ramp height?
You can measure the time taken to cover 1 m as the marble leaves the ramp.
The average speed can then be calculated from speed = distance/time
Initial considerations: What is the independent variable?
What is the dependent variable?
What are the control variable?
How many repeats are needed?

10. Plot a graph of average speed against ramp height
Investigation: How does the speed of a marble leaving a ramp vary with ramp height?
Plot a graph of average speed against ramp height