Objectives:
1. How can you measure the work which is done?
2. How does the work in each case relate to the change in the energy of each system.
3. How can you measure the energy of each system so that it can be compared to the work that was done?
Key Terms:
- Force
- Gravity
- Mass
- Work
Pre Lab Discussion:
This lab involved an introduction to Work and Kinetic Energy. The following screenshots will provide an overview:
Materials:
- Force Probe
- LabQuest
- Motion Detector
- Spring
- 500g Weight
- Vernier Car
Procedure:
Spring
1. Attached force probe to spring, zero probe
2. Stretch and displace spring; record data
In our experiment, the spring was displaced 0.05 m. We recorded the elastic potential energy in this graph:
Weight
1. Place weight on the floor
2. Attach force probe to weight, zero probe
3. List weight from floor to chair, about 0.5 m
4. Record data
In our experiment, the 500g weight was lifted 0.5 m. We recorded the gravitational potential energy in this graph:
Car
1. Change attachment on force probe
2. Place car at the very beginning of track
3. Place motion detector on opposite end of track
4. Push car for a few seconds, drop force prob directly on the track
5. Stop the car before it collides with motion detector
6. Record data
In our experiment, the car was displaced 0.15 m. We recorded the results of the experiment in this graph below:
So let's go back to our essential questions:
1. How can you measure the work which is done?
2. How does the work in each case relate to the change in the energy of each system.
3. How can you measure the energy of each system so that it can be compared to the work that was done?
Analysis:
1. We can measure the net work which is done on the entirety of a system by using the formula:
W= Fcos(theta)*delta x. In our experiments, the force is parallel to the direction of the displacement. In these experiments, theta is equal to 0 degrees (or 180 degrees), meaning the cosine is 1. As long as this is a true, then the formula simply becomes W = F*delta x. The force for our calculations was found using the mean of the force graphs for the weight, spring, and car. The displacement was measured in meters. Here's the math:
Weight:
W = (0.5kg)(9.8m/s^2)(0.5m)
W = 2.45 J
Spring:
W = (5.857N)(0.05m)
W = 0.293 J
Car:
W = (0.7 N)(0.15m)
W = 0.0105 J
2. The net work on a system is equivalent to the change in kinetic energy of the same system. If work is done on a system in the direction of the motion, the system will have an increase in kinetic energy. If work is done on a system against the direction of motion, the system decrease in kinetic energy.
3. The kinetic energy of a system is found using the formula KE = 1/2*m*v^2. Once you find the kinetic energy of the system, you can compare it to the amount of work you have done on the same system.
