EXPERIMENT: GRAVITY
Here are your goals for this lesson:
Calculate the change in potential energy and weight
Record the results in a report
In this experiment, we will use a magnet to simulate the amount of gravity exerted on a suspended object by a nearby mountain. This experiment will measure the change in potential energy as the washers are pulled toward the magnet. Potential energy is the energy an object has to its height above a given reference point, such as a table or the floor.
Materials needed:
Magnet
Long string, approximately 1 meter
Several washers, or other materials that would be attracted by a magnet
Meter stick or ruler
Balance
A blank piece of card stock or paper to place behind the washers and string
Procedure:
1. Determine the mass of the washers. (These will be suspended by the string.)
2. Suspend the washers from one end of the string.
3. Hang the string from a place where it can swing freely, such as from a tripod or doorway. See the illustration below.
4. Fix the card stock behind the washers in such a way as to be able to mark the height of the washer above the table or floor. Make sure the card stock comes to the table or floor. (Using the card stock will make getting these measurements a little easier. Mark the spot and then measure the distance from the card stock.)
5. Measure the distance of the suspended washer to the floor or desktop (D1). Record this distance in your REPORT document.
6. Move the magnet toward the washer until the washer begins to move toward the magnet.
7. Adjust the distance of the magnet from the washer until the washer hangs freely toward the magnet in a suspended state. Do not let the washers stick to the magnet. This part of the experiment is a little tricky.
8. Carefully measure the distance once again from the floor or desktop to the new position of the washers (D2). Record this distance in your REPORT document.
Analysis:
To find the force exerted on the washers by the magnet, we must first find the weight of the washers. Note: the gram is not a measurement of weight, it is a measurement of mass. To convert mass to weight, we must use the formula:
W = mass x gravity
Once this is determined, then calculate the difference in potential energy created by the magnet by using the equation:
Potential Energy = Force x Distance
To show you how this works, study the following example.
If the washers had a mass of 2 grams, and since the force due to gravity in the metric system is 9.8 m/sec2, the weight would be:
W = mass (kg) x gravity
W = 0.002 kg x 9.8 = 0.0196 Newton's. The newton (N) is the measure of force (or weight here) in the metric system.
The next phase of the computation is to determine the difference in potential energy between where the washers originally started and the energy of the new position. If the washers were originally 1 meter from the floor or desktop, and the magnet raised them 1 centimeter, the difference in distance raised will be 1 cm or 0.01m. Therefore, the potential energy change will be:
Force x Distance = Potential Energy
(0.0196N) x (0.01m) = 0.000196 Nm (or joules)
The magnet is changing the potential energy of the washers by 0.000196 J, or in scientific notation:
1.96 x 10-4 J.
By following this example, do the computations and record your results on your REPORT document.
