Application Projects
Just as important as understanding physics concepts is understanding how to apply them. To this end, there will be five mini-projects that involve applying physics concepts from class to real-world situations. These will require you to spend time outside of class taking measurements and making calculations. In general, the equipment required for these projects will be very simple. You can borrow the following equipment from Kristine: stopwatches, tape measures, protractors, and a bathroom scale. Because there is no lab fee for this class, any lost or damaged equipment must be replaced by you. Because of the nature of the measurements needed for these projects, you are highly encouraged to work with a partner. However, you should all take your own data (no duplicate data!) and do your own analysis.
The instructions for these application projects are given below. You should turn in your responses to all questions along with any relevant data and calculations.
Application Project 1: Measure your car's acceleration
(due in class on 4/13)In this project, you'll apply kinematics to measure the acceleration of your car. First, come up with a procedure for measuring your car's acceleration. Think about equations we've covered that involve acceleration and what quantities would need to be measured to calculate acceleration. We have stopwatches you can borrow if needed. If you have access to an accelerometer, you can use that for the extra credit portion of this project but not for the main measurement.
* Question 1 (5 pts) - Describe in a few sentences your method for measuring your car's acceleration. Include relevant equations and descriptions of quantities you will measure and what you will use to measure them.
On a safe stretch of empty road, start from rest and quickly press your car's gas pedal down halfway (if you floor it your tires will skid and your measurements will be off). You aren't measuring your car's top acceleration, just an acceleration. Measure your car's acceleration using the method you outlined in question 1. NOTE: It is not safe to take data for this project while driving so please work with a partner! Do not use this project as an excuse to drive unsafely.
If you do not have a car you should either 1-make friends with someone who does or 2-ride the bus and measure the bus' acceleration.
* Question 2 (5 pts) - What is your car's acceleration? Make a table with your data and show your calculations. Please also write down what type of car you have and how many people were in the car during data taking.
* Question 3 (5 pts) - Is your measured value a sensible answer? Explain how you know. (Don't just re-explain your math; compare this value to other known accelerations to confirm that your value is not too high or too low.)
* Question 4 (10 pts) - Is your car's acceleration constant? To answer this question, devise a new experiment to test this. Describe your experiment and your results.
* Question 5 (5 extra credit pts) - If you have access to an accelerometer, use it to confirm your results for questions 1-3. Write a paragraph discussing how well the measurements agree and possible sources of error (Note: human error implies that you've messed up in measuring and should have done the experiment again. If that's the case, you probably won't get the full 5 pts of extra credit.)
Application Project 2: Measure the elevator's acceleration
(due in class on 4/27)In this project you'll apply Newton's 2nd law to measure the acceleration of the Whitehorse Hall elevator going from the 2nd floor to the 3rd and back again. There is a force probe outside of Kristine's office (WHI 216). Note that there is acceleration when the elevator first starts going and again when it slows down. You will measure both of these for the trip up and the trip down. Also note that pounds are a measure of force, not mass.
* Question 1 (10 pts) - Draw free-body diagrams for four following different periods of acceleration: when the elevator is leaving the second floor, when it is arriving at the 3rd floor, when it is leaving the third floor and when it is arriving back at the second floor. For each FBD, also include a net force vector off to the side.
* Question 2 (10 pts) - What is the elevator's acceleration during these four different phases? Make a table with your data and show your calculations.
* Question 3 (5 pts) - Is your measured value a sensible answer? Explain how you know. (Don't just re-explain your math; compare this value to other known accelerations to confirm that your value is not too high or too low.)
* Question 4 (5 extra credit pts) - While accelerating from rest, does the elevator's motor supply a constant acceleration, constant force, or neither? To answer this question, devise a new experiment to test this. Describe your experiment and your results.
Application Project 3: Measure the tension in a string for circular motion
(due in class on 5/11)In this project you'll apply Newton's 2nd law in two dimensions and concepts of circular motion to measure the tension in a string when used to spin an object at a constant speed. There are stopwatches, tape measures and protractors available for check out if needed. If you need to weigh something you can drop by the physics lab during open lab times to use a scale. You will need to take a photograph of this experiment so it is recommended you work with a partner. Between the two of you, someone will likely own a digital camera or a cell phone with a camera built in.
First, find some string of negligible mass. Tie a mass to the end of this string. It should be massive enough that it is not easily slowed by drag but not massive enough to be dangerous. You'll be spinning this mass on a string in horizontal circles. But you should swing slowly enough that the string does not appear to be horizontal.
* Question 1 (5 pts) - Draw two free-body diagrams for the mass: one as viewed from above and another as viewed from the side. Include a separate net force vector.
Swing the mass on the string around over your head at a constant rate. Your results will come out better if you don't swing it at a deadly speed. Measure this rotation rate and be sure to keep it constant. Your partner will need to photograph you and the string in profile during this motion so you can measure the angle the string makes with the horizontal. You may need to take several pictures to get one that shows the string perpendicular to the camera's field of view. Be sure the camera is level. If the string appears to be totally horizontal, swing it slower. If you can't seem to get a picture of the string at the right time, consider using a longer string.
* Question 2 (5 pts) - What are the mass, radius of rotation, angle from the horizontal, frequency, velocity and angular velocity of the mass on the string? Make a table with your data and show your calculations.
* Question 3 (10 pts) - What is the tension in the string? Show your calculations. Keep in mind that the string is not perfectly horizontal, so the angle should be part of your calculations.
* Question 4 (5 pts) - Is your measured value a sensible answer? Explain how you know.
* Question 5 (5 extra credit pts) - In reality there is a drag force present, which requires you to apply a little force that is not in the radial direction to maintain this constant circular motion. Estimate the magnitude of this drag force and describe its effect on the mass's motion and the string's tension if you were to stop applying a non-radial force. Include in your explanation a revised free-body diagram.
Application Project 4: Propel something upwards with a spring
(due in class on 5/26)In this project you'll apply concepts of work and energy to measure the initial speed of an object propelled upwards by a spring and to confirm the conservation of mechanical energy. There are stopwatches and tape measures available for check out if needed. If you need to weigh something you can drop by the physics lab during open lab times to use a scale.
First, find a spring or rubber band and a mass.
* Question 1 (5 pts) - Devise a method for measuring the spring constant of your spring or rubber band. Describe your method, perform the measurement and report your answer along with any measurements you took and calculations you made.
* Question 2 (10 pts) - Use the spring or rubber band to propel the mass directly upwards. Calculate the intial and final mechanical energies of the mass-spring system. Make a table of any measurements you need to take to calculate these energies and show your calculations.
* Question 3 (5 pts) - What is the mass's velocity just as it leaves the spring or rubber band?
* Question 4 (5 pts) - Was mechanical energy conserved during the mass's launch and motion upwards? Refer to your data in your answer.
Application Project 5: Measure the period of a playground swing
(due in class on 6/8)In this project you'll apply concepts of simple harmonic motion and the physics of a pendulum to a common piece of playground equipment. There are stopwatches and tape measures available for check out if needed. If you need to weigh something you can drop by the physics lab during open lab times to use a scale.
First, find a playground with a swing, preferrably at a time when you don't have to compete with children for its use. Measure the radius of the swing.
* Question 1 (5 pts) - What is the natural period for the swing? Show your calculations.
* Question 2 (5 pts) - Swing for a while at angles less than 15o and measure the period of the swing.
* Question 3 (5 pts) - Do your calculated and measured values agree? If not, give possible reasons why. Again note that if you claim there was human error that means you should redo the experiment or lose points.
* Question 4 (10 pts) - What if you stand on the swing instead of sitting? Do this and measure the period of your swinging. Compare this period to the period obtained from sitting. If they do not agree, give a possible explanation as to why.