Physics Review With Simulations

1. Linear Kinematics – Use the PhET simulation The Moving Man.  Experiment dragging the man back and forth on the number line.  Check the boxes to show the Velocity Vector and the Acceleration Vector.  Notice the controls at the bottom that allow you to record and playback the motion of the man.  You can also Clear a previous recording or Reset all of the program values.  At the top of the page there is a Charts tab that gives you access to graphs of position, velocity, and acceleration.
(a) Make a recording of the man moving back and forth, both slow and fast, steady and jerky.  Then view the recording in slow motion playback and observe the velocity and acceleration vectors – in what circumstances do these two vectors point in the same direction?  opposite direction?
(b) Try clicking and dragging in such a way that it is a constant velocity and use the playback features to see how constant the velocity was.
(c) Try clicking and dragging in such a way that it is a constant acceleration and use the playback features to see how constant the acceleration was.
(d) Reset everything and go to the Charts tab.  Make sure the program is paused and clear any recordings.  Enter values in the boxes on the left side:  position = – 10 m, velocity = 12 m/s, and acceleration =  –3 m/s².  Before you click on the play button use kinematics equations to calculate and predict the time and final velocity for the man to cross the screen and reach the position +10 m.  Then check your prediction by clicking the play button.  You can zoom in on the graphs and also playback in slow motion.
(e) Make another prediction: Again use an initial position of –10 m and acceleration  –3 m/s² – calculate an initial velocity that will cause the man to go only to the position +7 m (and avoid hitting the brick wall)?  And if this initial velocity is used, what total time will go by before he returns to his starting position?  Use the program to test and check your solution.

2. Linear Kinematics and Forces – Use the PhET simulation The Ramp.  Use the default object, the filing cabinet with mass 100 kg and μ = 0.30, and the default angle of incline 10°.  The ramp is 15 m long.  Play around with the controls – there are many options!
(a) On separate paper calculate the time it will take to move the filing cabinet all the way up the ramp starting from rest if a force of 600.0 N is applied parallel to the surface. 
(b) Test your predicted time with the simulation:  Move the object to the bottom of the ramp (you can use the position slider control and set it to zero).  Enter the applied force into the box on the left side of the simulation window and run the simulation.  You should be able to judge the time by the graph and other info on the screen.   Also look at the force values shown – are these the same ones you calculated?
(c) If the simulated person keeps pushing he runs into a wall at the top of the ramp and the force of the wall is shown – can you figure out where that value is coming from?  Can you calculate it yourself?
(d) Determine the kinetic energy at the top of the ramp using work and energy calculations.  Then compare to the values shown in the energy and work graphs.
(e) Put the object at rest in the middle of the ramp with zero applied force.  Now experiment by trial and error with applied forces (can click and drag) to find the amount of force necessary to start the object moving in either direction on the ramp.  Why is there a range of values for the applied force that will not move the object?  Can you calculate using the given numerical values the applied force that is required to move the object up the ramp?  down the ramp?

3. Vector Addition – Use the PhET simulation Vector Addition.  Click and drag to place two vectors on the workspace.  Check the box to Show Sum.  Also check the box to Show Grid.  The green arrow is the vector sum of the other vectors that have been placed on the workspace.
(a) Verify the head-to-tail rule by arranging the vectors – this can be done by dragging the arrows. 
(b) Try clicking and dragging the head of one of the red vectors – experiment and verify that no matter what vectors are added the green sum vector always follows the head-to-tail rule.
(c) Experiment with the program and verify by calculation the meaning of the values shown at the top:  |R|, θ, R_x, R_y.  What do these values represent?  Why use the symbol R?  Why the absolute value symbols?  Does the program use the same system for angles that we have used in class?
(d) Observe the different Styles that the program offers for Component Display.  Set up a vector addition example in which at least one of the values R_x, R_y is negative.  Then check the calculations that have been done by the computer:  add the components of the red vectors to find the components of the green vector and then use the Pythagorean theorem and a trig function to determine the direction angle. 

4. Projectile Motion – Use the PhET simulation Projectile Motion.  Click and drag the cannon and lift it up on its platform to a height about midway up the screen.  Enter values of your choice for the initial speed and direction of the cannon.  You can also choose your projectile object!  Use the simulated “tape measure” to determine the height of your platform.
(a) On separate paper calculate the range and maximum height of the projectile based on the numbers for initial speed and direction and the height of the platform.
(b) Test your prediction by clicking and dragging the “bull’s eye” target to the spot where you calculate it will land – use the tape measure to do this.  Fire the projectile.  Notice the time and position values that are shown by the program.  Do these match what you calculated?  Measure the height of the path shown and compare to your calculated value.
(c) Experiment with air resistance.  Can you get a projectile to reach a terminal velocity?  How can you tell?

5. Circular Motion and Universal Gravitation – Use the PhET simulation My Solar System.  Experiment with the controls and various “Presets”.  Notice that you can click and drag to move objects or change the initial velocity.  Turn all four of the “check boxes” ON.  Now set the simulation for two objects with these values: 
body 1:  mass = 200, x = 0, y = 0, v_x = 0, v_y = 0 
body 2:  mass = 0.1, x = 200, y = 0, v_x = 0, v_y = 110
(a) Run the simulation and observe the orbit.  Experiment by trial and error until adjusting the initial speed of body 2 until you can achieve a circular orbit.  Notice the elapsed time for one complete orbit.
(b) Use the radius of the circular orbit and the period to calculate the speed – does it match what shown in the table?
(c) Use the values describing this orbit to solve for the universal gravitational constant G that is used in this program. This will not equal the usual value we are familiar with because the program uses arbitrary units for mass, distance, and time (i.e. the values shown in the program are not based on kilograms, meters, and seconds).
(d) Take the value you found for G in the previous step and use it to calculate the correct missing value below that will result in a circular orbit:
body 1:  mass = 300, x = 0, y = 0, v_x = 0, v_y = 0 
body 2:  mass = 0.1, x = 0, y = 150, v_x =   ?  , v_y = 0
After you calculate it – set it up and simulate it and see if it works.
(e) Experiment with the mass of body 2, without changing the mass of body1.  Try smaller masses and larger masses – you should see little effect on the orbit unless it is made significantly larger.  Can you explain why?
(f) Challenge problem – again calculate missing values that make a circular orbit, but this time in a counterclockwise direction:
body 1:  mass = 200, x = 0, y = 0, v_x = 0, v_y = 0 
body 2:  mass = 0.1, x = 100, y = 150, v_x =   ?  , v_y =   ? 
Note:  solving this problem requires use of components and vector properties!

6. Circular Motion and Gravitation – Use the program iSat from NASA.  Experiment with the controls of the program and notice that there are a wide variety of satellites to choose from.  Under Globe Display you may want to use Arc GIS to get a better view of earth.  When you click on a satellite you can see its orbit and other information.  Pick a satellite with a circular orbit and then take the given altitude and use it to calculate the speed and period of its orbit and compare to the values shown.

7. Conservation of Energy – Use the PhET simulation Energy Skate Park.  Experiment with the program controls and graph options.  Create a track of your own design in which the skater will roll back and forth smoothly without leaving the track.  Set the friction to zero.
(a) Use the grid and/or tape measure to determine the maximum and minimum heights of the skater as he/she rolls back and forth.  Calculate the potential energy at these heights.  Use conservation of energy to calculate the kinetic energy that should occur at the minimum height.  Use the program tools to check your work.
(b) Try adding friction to the simulation and observe the changes that occur.  Use information from graphs, grid, measuring tape, etc. to determine the coefficient of friction that is being simulated (a value that is not shown to the user).  Is it a reasonable value for a coefficient of friction?
(c) Change the track to create a “ski jump” for the skater, such that you can release the skater from rest at the top of the track and then the skater will fly off the other end.  Measure the dimensions of the track and then use conservation of energy to calculate the “launch velocity” of the skater flying off the end.  Use this launch velocity to also calculate some measureable aspect of the skater’s motion after he/she leaves the track (such as range or maximum height.  Then run the simulation to check your answers.

8. Conservation of Energy & Simple Harmonic Motion – Use the PhET simulation Masses and Springs.  Try hanging different masses on different springs and observe the results. 
(a) Hang one of the known masses on spring 1 and let it come to a complete stop, hanging at rest.  Use the tools of the program to measure the amount that the spring is stretched by the weight of the object.  Calculate the value of the spring constant k.  Repeat with different masses and solve again for the spring constant.  Is it constant?
(b) Calculate the period of one of the given masses oscillating on the end of spring 1.  Set friction equal to zero.  Then simulate this oscillation and determine the period using the program’s simulated stopwatch.

9. Electrostatics – Use the PhET simulation Charges and Fields.  Drag any number of charges onto the workspace.  Use the controls to Show Grid and other features.  Click and drag an E-field Sensor to explore the field created by the charges.
(a) Reset the program and then place two positive charges somewhere on the grid.  Make them different amounts – by stacking 1 nC charges directly atop one another you can make any multiple of nanocoulombs.  Pick a location anywhere on the grid and use physics to calculate the electric field that should result from the two positive charges.
(b) Reset the program and then place a charge of +4 nC at the far left side of the grid and a charge of –1 nC at a position 1.0 m to the right of the positive charge.  Use physics to calculate where on the grid the net electric field would be zero.  Check your answer with an E-field Sensor.  Now drag the E-field Sensor to a position at which the field points directly upward and then try calculating this same field based on the position of the Sensor.

10. Circuits – use the program DC circuit construction kit.  Click and drag to form any possible circuit consisting of resistors, batteries, switches, and light bulbs.  Each element can be customized by right-clicking to change its properties.
(a) Reset the program and create a circuit consisting of two batteries and three resistors of three different values.  Make sure that current flows through each resistor.  Calculate the voltage and current for each resistor and the check your result using the meters in the program.
(b) Experiment with the Advanced settings and give the wires a small amount of resistance.  Try setting up a simple circuit with a single battery and a single resistor.  Rotate the resistor so that it is oriented perpendicular to the battery – this will make the wires different lengths.  Use the voltmeter to measure the voltage drop across the wires.  Calculate the resistance of each wire based on its voltage and current.  Calculate the effective resistance of the whole circuit by treating the wires as two additional resistors.  Does the current in the circuit correspond with this effective resistance as expected?  Calculate and check.  Try a similar exercise with a simple parallel circuit in which wires have a small amount of resistance.