Describing Motion

What is speed?• Think of the fastest and slowest speed limits near

the school, on the roads in front of your homes, or on a highway.

• What units are speeds measured in?

• So, what is speed?

• Speed – distance an object travels over a certain amount of time

Speed• The distance an object travels in a certain amount of time.

– Average speed – Total distance divided by total time– Constant speed - Speed that does not change

– Give an example.

What is velocity?

•Velocity – an objects speed and direction at a given instant.

Velocity

• An object’s speed and direction at a given time– The wind is blowing 65 km/hr from the North.

Give an example of your own.

So, What is acceleration?

•Acceleration – change in an

objects speed or direction over time.

Acceleration• A change in the direction or speed (velocity) of an object

over time – which may be:– A change in speed• Starting• Stopping• Speeding up (positive acceleration)• Slowing down (negative acceleration)

– A change in direction• Acceleration is caused by unbalanced forces.• On your paper, describe an example of an object

accelerating.

What is the formula for calculating speed?

Speed equals distance divided by time.

Check Your Work

A football field is about 90 meters long. If it takes a person 30 seconds to run its length, how fast was the football player running?

–Speed = Distance ÷ Time

–Speed = 90 m ÷ 20 s–Speed = 5m/s

Remember to label the UNITS!!

Let’s Practice Calculating Speed

A football field is about 90 meters long. If you run it at 2m/s, how long would it take you to run the length?

On the back of your sheet, calculate this problem. Make sure you show all work!

Interpreting the Graph

Interpret the Graph Below:

The graph shows an object which is not moving (at rest).

The distance stays the same as time goes by because it is not moving.

Interpret the Graph Below:

The graph showsthat the objects distance increases as time passes.The object is moving and so it has velocity.

The straight line shows it is a constant (not changing).

Interpret the Graph Below:

Just like the previous graph, this graph shows an object moving with constant velocity.

Interpret the Graph Below:

The curve, in the graph, shows that the object’s velocity is changing as time passes.

This is acceleration.

Interpret the Graph Below:

In the first part of the graph, the object is moving with constant velocity. (A)

In the second part of the graph, the object is at rest (not moving). (B)

In the third part, the object is again moving with constant velocity. (C)

A

Practice

1. S = 60 cm/s, d = 15 cm, t = ?

2. d = 300 m, t = 62s, s = ?

3. s = 42 m/s, t = 2.3 s, d = ?

• Using the Cheetah Hunt Graph:

1. Find the velocity for each segment.

2. Find the average speed.

Story Graphs

From the graph given( Fourth Walker):• Write a story to correspond with each graph

(Use the Cheetah story as a guide)• Include:–1. Distance and time between

acceleration points.

2. Velocity between acceleration points

• 3. Average speed