Material

Three People: one to ride the wheeled board, one to run the stopwatch, one to drop the beanbags. A skateboard ($10 at Walmart)

Optional build your own, buy a redwood barrel roller from Orchard Supply mount a 20+ inch 3/4 inch thick disk onto the roller.

A room with a smooth hard floor

five or more beanbags

A stopwatch

A springscale (able to apply 50 N or 10 lb. of force)

a bathroom scale

A backpack full of books

A meter tape

To Do and Notice

Have a person put on a backpack full of books and hold the skateboard
find the mass using the bathroom scale.( Recall that on earth there is a force of 1 pound on 0.45 kg, so that 2.2 lb. = 1 kg)

Thus a 165 pound person plus gear masses 75 Kg, 165 lb. * 1 Kg/2.2 lb.

Place a beanbag next to the person sitting at rest on the rolling platform or skateboard.
Start pulling the person with the scale reading 25 N.

At the same time start the stopwatch.

Have the beanbag person drop a beanbag next to the skateboard every second. Have the stopwatch person call out the seconds.

After five seconds stop the data taking.

Use the meter tape to measure the position of each beanbag with the initial beanbag as the origin of the measurements.

Plot the positions of the beanbags versus time.

What's Going On?

A constant force will produce a constant acceleration.

Newton said it as one of his laws of motion:

F = ma which is the same as a = F/m

The acceleration of a 75 KG person under a 25 N applied force is

a = 75 Kg/25 N = 3 m/s^2

In the absence of friction.

A constant acceleration of 3 m/s^2 will produce distances versus time of

t s	d m
0	0
1	1.5
2	6
3	13.5
4	24

Going Further

Plot your data as distance versus time on graph paper.

Optional Construction

Build your own roller cart

Wheels for a redwood barrel screwed onto a 24 inch particle board disk.

Screw a redwood barrel roller system onto the bottom of a particle board disk about 24 inches in diameter.

Scientific Explorations with Paul Doherty

© 2004

8 October 2004