Materials:
- a toy car
- balance
- masses of known mass
- ruler
- string
Procedure:
1. Find a toy that moves with little resistance. Check this by rolling along a smooth counter top to determine if it coasts at nearly constant speed as would be expected by Newton's first law.
2. Find several lighter objects of known mass (in grams), perhaps a box of labelled jello, or a small candy bar. This will be used to provide a known force.
3. If you don't have a balance to find the mass of the toy, use a ruler for a make-shift balance. Hold the ruler by a string through its middle, hang an object of known mass from one end of the ruler like in the picture, and find the location for hanging the toy that just balances the known mass. The product of the known mass times its distance to the middle must equal the mass of the toy and its distance to the middle: m1 x d1 = m2 x d2. Solve the equation to find the mass of the toy.
4. Connect the toy with the known mass by a string passing over some object that allows the string to move with little friction.
5. Let the known mass accelerate the toy.
6. Measure the time interval between the release of the mass and the time it hits the floor.
7. Measure the distance the toy car travels from the front of the car.
8. Use the formula d = 1/2 at^2 to determine the acceleration.
9. Determine the force pulling the toy using the formula, F = mg.
10. Note that both the toy and the pulling mass are tied together and both move as if there were one body due to the weight of just the known mass. So add the mass of the toy to the pulling mass, m.
11. Use the formula F = ma to see if it is equal.
12. Change the known force pulling on the toy to determine if acceleration is proportional to the force.
13. Change the mass of the toy by attaching known masses to determine if acceleration is inversely proportional to the mass.
