WORK PRE-LAB QUESTIONS: 1. List the equation that represents the relationship between work, force, and displacement. 1a. Write the equation that represents the relationship between Power, work, and time (+1 bonus point if you can rewrite the equation 3 different ways). 2. A hill has three paths up its sides to a flat summit area, point D. The three paths lengths AD, BD, and CD are all different, but the vertical height is the same. Not including the energy used to overcome friction, which path requires the most work to achieve the summit? Use full sentences to answer. 3. A mass of 0.5-kg is lifted up a height of 0.2m. How much force is the weight of the object? 4. How much work is done on the object? 5. Is it positive or negative work? 1
6. If it is accomplished in 3 seconds, how much power was needed? WORK OBJECTIVE: Explore the relationship between work and kinetic energy. Verify the Work- Energy theorem by experimentally determining the work done on a glider by a launcher. INTRODUCTION: When work is done on an object, energy is provided to that object in the form of kinetic energy. Work done on an object by a force is defined to be the product of that force that is parallel to the objects displacement and the displacement itself. W = F*d where F is any force or component of a force that is parallel to the objects displacement, and d is the displacement of the object while the force is applied. We find tasks difficult when we must apply a large force, such as when we lift a heavy weight or need to overcome a large amount of friction. As our brains are much larger than the majority of muscles in our bodies, we have used it to overcome these difficulties. Using physics we have developed what are called simple machines. What are Simple Machines?! Simple machines help to decrease the amount of force needed to do work by increasing the distance over which the force is applied. The example from the video shows Mr. T reducing the amount of force needed to lift two books by using a lever and fulcrum. The concept behind this is shown here in figure 2 You will be using two other kinds of simple machines and testing the work/energy theorem for yourself. The first is called an incline plane (Ramp) [Figure 1]. The ancient Egyptians were thought to have used this technology to help them construct the great pyramids and we still use it today! The second machine is known as a lever (figure 2). Levers produce a bigger force than the force you apply. To better explain, with a long lever, you can exert a lot of leverage. An example would be when you use an axe, the handle helps you magnify the force you apply. 2
Figure 1 Figure 2 MATERIALS: The materials should be set aside at a station, It should include the following: 2 Meter stick Balance Clamp 3x 200g masses PROCEDURE 1: Spring scale Binder clip Cart Track 6x text books 1. Slide the meter stick into the clamp and move the clamp to the midpoint (50 cm). 2. Place the meter stick on the balance and attach the masses to the end reading 0 centimeters *You will be recording data from three different arrangements for procedure 1 (See figure 3) 3a. Arrangement A the clamp should be centered on 25 cm 3b. Arrangement B the clamp should be centered on 50 cm 3c. Arrangement C the clamp should be centered on 75 cm 4. Using the spring scale, pull up or down to lift the weight to its maximum height 5. In Table 1, Record the force and distance from both the 0cm and the 100cm sides of the meter stick. 3
* Force is measured in N while distance is measured in meters (cm/100) (See figure 4). LIFT SLOWLY!!!!! Table 1 Arrangement A (Fulcrum @ 25cm ) Arrangement B (Fulcrum @ 50 cm) Arrangement C (Fulcrum @ 75cm) 0cm side 100cm side 0cm side 100cm side 0cm side 100cm side Force (N) Distance (m) Work done (J) PROCEDURE 2: 1. Remove the mass from the meter stick and set both aside and stack the 6 books close to one edge of your desk. 2. Place the mass in the car 3. You will be recording data from three different arrangements (See figure 5) 3a. arrangement D the feet are at 100cm on the track. 3b. arrangement E the feet are at 75cm on the track. 3c. arrangement F you use no track at all and lift the cart vertically to the top of the books. * You will STOP TAKING MEASUREMENTS when the carts center has reached the top of the stack of books 4. Using the spring scale, pull the cart until its center matches the top of the books. (See Figure 5) 5. Record the force and distance from the carts starting location to its ending location (Table 2). * You will measure force (N) with the spring scale and distance (m) using the track or a meter stick. 4
Table 2 Arrangement D Arrangement E Arrangement F Force (N) Distance (m) Work done (J) Long ramp (100 CM) Short ramp (75 CM) No ramp ( CM) Post Lab Questions: In Table 1. Indicate when work is equal. Why? Have you ever used a lever and fulcrum to help you do more work with less force? Provide an example? What is one simple machine we believe the Egyptians used to help build the machines? How was this machine effective in making the work easier for them? 5
Identify at least two trends EACH that you observed in data tables 1 & 2. Table 1: Table 2: Identify potential scientific error when running your experiment. What would you do different to mitigate this type of error in the future? In Table 1, which trial would be more powerful if: arrangement A was lifted in 3 seconds, arrangement B was lifted in 1 second, and arrangement C was lifted in 5 seconds? SHOW YOUR CALCULATIONS. Arrangement A: Arrangment B: Arrangment C: In Table 2, which trial would be more powerful if: arrangement D traveled up the ramp in 7 seconds, arrangement E traveled up the ramp in 4 seconds, and arrangement F traveled up the ramp in 6 seconds? SHOW YOUR CALCULATIONS. Arrangment D: Arrangment E: Arrangment F: 6