Frictional Force (32 Points)

Transcription

1 Dual-Range Force Sensor Frictional Force (32 Points) Computer 19 Friction is a force that resists motion. It involves objects in contact with each other, and it can be either useful or harmful. Friction helps when you want to slow or stop a bicycle, but it is harmful when it causes wear on the parts of a machine. In this activity, you will study the effects of surface smoothness and the nature of materials in contact on sliding friction. You will use a computer-interfaced Force Sensor to measure frictional force, in Newtons (N), as you pull a block across different surfaces. OBJECTIVES In this experiment, you will Use a computer to measure sliding friction. Measure friction between a wooden block and smooth-surface wood. Measure friction between a wooden block and rough-surface wood. Make predictions about other surfaces. Test your predictions. MATERIALS computer Vernier computer interface Logger Pro Vernier Force Sensor wooden block (with a hook) wood with smooth surface wood with felt surface cart Figure 1: Using the Dual-Range Force Sensor Physical Science with Vernier 19-1

2 Computer 19 PROCEDURE Part I Smooth and Rough Surfaces 1. Get a wooden block (with a hook on one end). Hook the block to the Force Sensor. 2. Prepare the Force Sensor for data collection. a. Open Logger Pro, open yellow folder on the top left, open Physical Science w Venier, open 19 Frictional Force. b. Connect the Dual-Range Force Sensor to the computer interface. c. Set the switch to the lowest setting. 3. Slowly pull the wooden block across a piece of wood with a smooth surface. Hold the Force Sensor by its handle and pull it to you, as demonstrated by your teacher. The Force Sensor should be held parallel to and about 2 cm above the surface. Once the wooden block is moving at a steady rate, click to begin data collection. 4. After the data have been collected, look at the graph displayed on the screen. If the graph is reasonably flat, proceed to Step 5. If there are big peaks and valleys, repeat Step Click the Statistics button,. Record the Mean (average). Enter the force in Newtons below, round to the first decimal (tenths). This is your control. DATA: CONTROL Surface Smooth side of wide wood Force (N) (2 points) Part II Predicting Friction 7. You will measure friction of the block as it s pulled across your desk top for the variables in the data table below. In the data table supplied below, Before you measure anything, first predict whether the force of friction will be greater or less than the control measured above. 8. Predicted order of Frictional Force values for eight variables that you will be testing. 9. Repeat Steps 3 5 for each of the surfaces, enter the data, accept or reject your prediction and explain your results for each test in complete sentences Physical Science with Vernier

3 Frictional Force Date Table 1: (16 points) Skinny wood edge Predict greater or less than control Measured (N) Rank the 8 variables in order of least to most Frictional Force (1-8) Explain Result and accept or reject prediction using complete sentences. Skinny purple edge wood planks on wide wood edge Single wood plank on metal cart wood planks on metal cart Wide wood edge up Wide wood edge up Your shoes Physical Science with Vernier 19-3

4 Computer 19 PROCESSING THE DATA (14 points) 1. Based on your data, what variables that you tested increased the friction measured using the Dual-Range Force Sensor? (2 points) 2. How did you decide the order of your predictions in Part II? (2 points) 3. How good were your predictions? Explain using the data in your data table. (2 points) 4. What factors do you think play a role in determining how much force is needed to pull something? (2 points) 5. Give two examples of situations where friction is helpful. (2 points) 6. Give two examples of situations where it is best to reduce friction. (2 points) 19-4 Physical Science with Vernier

5 Frictional Force 7. Summarize the results of this experiment. (2 points) EXTENSIONS 1. Test the friction of other surfaces, such as glass, metals, rubber, and different fabrics. 2. Investigate how frictional force varies with contact area and mass. 3. Design an experiment to test methods of reducing friction. Physical Science with Vernier 19-5