Return to Physics IndexStraight Line Motion in Two Parts

Ann M. W. Brandon Joliet West High School

401 N. Larkin Ave

Joliet IL 60435

(815) 727-6950Objectives:

Students will observe both constant and accelerated (changing) motion.

They should be able to calculate speed from distance and time measurements.

They will graph distance vs time for each motion and observe that the two

motions look different when graphed. This was designed for upper middle school

to 9th grade students.Materials Needed:

Per group of 2 or 3 students:

Stomper (battery powered toy car)

Stopwatch, or second hand on a clock

Meter Stick

Toy car, not powered

A long slope (a table with two legs propped up with some books)Strategy:

Part I: Stomper

Issue a Stomper, stopwatch, and meter stick to each lab group.

Ask the following questions, in writing:

Describe the motion of the car as it rolls along the table.

How can you tell what it is doing?

What do you need to know to find the speed of your Stomper?

Find the average speed of your stomper over a distance of 1 meter.

What can you measure? How many trials should you try?

Record your measurements and calculations.

Is this a constant speed? How can you tell?

Find the average speed for 2 meters.

Was it the same as the average speed for 1 meter?

What about 3 meters?

Graph the Distance Traveled vs the Time Taken for 1, 2 and 3 meters.

Describe this graph.

Is it straight?

Is this constant motion or changing motion?

What is the relationship between the Distance Traveled and the Time Taken?

Look at the slope (rise over run) of the graph, and calculate this slope.

What does this tell you?

Part II: Car Rolling Down Hill

Trade the toy car for the Stomper.

Help your students create a hill.

Ask your students the following questions, also in writing.

Start your car at the top of the hill.

Describe its motion.

Is it constant motion? Or is it accelerated (changing) motion?

Find the average speed of your car for 1/2 meter.

Record your measurements and calculations.

Repeat for 1 and 1 1/2 meters (or the end of the hill)

What do these speeds tell you? Is it constant motion, or accelerated

motion?

Graph the Distance Traveled vs the Time Taken.

Describe this graph. Is this a straight line?

What does this graph tell you about the motion of the car rolling down the

hill?Performance Assessment:

Two possible follow up assessments:

1. Use a "Two Speed" Friction powered car. Wind it up and let it go.

Ask for descriptions of its motion. Then ask for a sketch of a distance vs

time. It will have a section of constant motion, then shift gears, accelerate,

and have a new, faster constant motion.

2. Draw a graph of some motion, and ask for a description of that

motion.Conclusions:

Students should be able to measure distance and time.

They should be able to combine them to find speed.

They should be able to graph distance vs time, and find the slope to find

the speed.

They should recognize the difference between constant motion and

accelerated motion.

They may even be able to tell the difference in the motions by the sound of

the cars as they roll along.