# Project #66192 - Physics lab help

Course PHY  101                Name         Date

PHET 4 Ramp: Forces and Motion

Explore forces and motion as you push household objects up and down a ramp. Lower and raise the ramp to see how the angle of inclination affects the parallel forces. Graphs show forces.

Learning Goals

• Predict, qualitatively, how an external force will affect the speed and direction of an object's motion.

• Explain the effects with the help of a free body diagram.

• Use free body diagrams to draw position, velocity, acceleration and force graphs and vice versa.

• Explain how the graphs relate to one another.

• Given a scenario or a graph, sketch all four graphs.

1. Joe is going off to college and is loading his file cabinet onto the moving truck by sliding it up a ramp like in the picture below.

a. Sketch (on paper, do not submit) what you think the free body diagram would look like for the file cabinet and explain your reasoning.

b. Use Ramp: Force and Motionto simulate Joe’s situation. Compare your free body diagram to the simulation and make any corrections to your drawing and reasoning.

c. Investigate the simulation to see what affects how hard Joe must push to move the cabinet up a ramp.

d. Describe your experiments and results, including description of the free body diagrams.

e. Draw (on paper) the free body diagrams for the cabinet if it were being pushed on a flat surface and if it were being lifted straight up. Compare those to the ones you observed on the ramp, and then describe the differences and similarities.

2. Next, Joe wants to load his crate of books.

a. Predict what you think the free body diagram would look like.

b. Explain what might cause similarities and differences between Joe moving the crate versus the file cabinet.

c. Test your prediction and thoughts using the simulation.

d. Describe your experiments and results including the free body diagrams.

Calculating the net force on an incline.

1.  Joe is moving his refrigerator to take to college and he begins by pushing it across the wooden kitchen floor.

On a flat surface like the floor, how do you calculate how hard he needs to push? Draw a free body diagram (on paper)  to help explain your answer and use the simulation Ramp: Force and Motionto check your ideas. Record the minimum force Joe would have to use to move the refrigerator on the kitchen floor.

1170.38 was the minimum applied force joe had to use in order to get the refrigerator to move up the ramp &   844.47 was the minimum friction force as if moved up the ramp

2.  Later, Joe is ready to load his refrigerator onto the moving truck.

a. Explain how he would calculate how much force to use to lift the refrigerator straight up into a truck.

b. Joe starts thinking about easier ways to get it in the truck and remembers he has some wood that he could use to make a ramp. How could he calculate the minimum force needed to push it up the ramp?

c. Use the simulation to check your ideas by running experiments with different objects at several angles. Make a data table including several trials with the calculations.

 Ramp angle Weight (Fg) Fgravity Ffriction Fapplied Resulting motion (stationary, down ramp or up ramp) Possible calculations to explain

QUESTIONS

Tips for controls:

ï‚· Game tab - use the keyboard arrow buttons to apply force to the object.

ï‚· Be sure to try all the different tabs at the top of the simulation.

ï‚· Use the controls on the bottom to Pause, Step, or Record and Playback the motion. You must select Record before you start an experiment if you want it saved.

ï‚· The vertical gray line in the graph is grabbable in Playback mode. It is useful to relate the object's motion to the graphs.

Important modeling notes / simplifications:

ï‚· Thermal Energy - the surface will heat up due to work done by friction. The friction coefficients do not change when the surface heats up.

ï‚· Using the "Clear Heat" button will remove the thermal energy. While the surface is wet (blue) the coefficients of friction are lowered until the surface is dry again (brown).

ï‚· If you want to explore how friction coefficient and mass effect friction forces, use the Friction Tab in the sim Force and Motion

Information regarding the game tab:

ï‚· In the game, the purpose is to use your experience from the other tabs to get objects into the house. Points are awarded based on use of energy.

ï‚· Some students may try to make changes while in the Playback mode and then hit Play; the sim will not run until Record is selected.

 Subject Science Due By (Pacific Time) 04/12/2015 06:00 pm
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