Academics

Energy

 

Physics Lab Manual

Turn on the ULI box which is connected to your computer. Connect a motion sensor into the ULI in Port 2. Log onto the computer and start the program "LoggerPro". (The ULI must be turned on before starting the program.) 

Under "File", click on "Open", "Experiments", "Physics with Computers", "Exp2", and then "Exp 2 Ball". This will load the software that will enable us to gather position, velocity and time information about any object the motion sensor sees. We will start by observing falling basketballs.

Freefall

Drop a basketball so it falls toward a motion sensor covered by a grid (to protect it). The ball must start as far from the ground as you can manage. (You can have one person drop the ball, another catch it just as it is about to hit the grid, and another start the program to record position and velocity information.)

1. What sort of energy does the ball have before it is released?

2. What sort of energy does the ball have when it is halfway to the ground?

Does it have more or less total energy than it had at the top before you released it?

3. What sort of energy does the ball have when it is just about to hit the ground?

Does it have more or less total energy than it had at the top before you released it?

Now, look at the data you collected for the falling ball. From this, you can find the speed of the ball at any position you like. The ground is zero height.

On the screen, you will see two graphs, one showing the ball's position as time goes by, and another showing the ball's speed as time goes by. To see all of the motion, you may have to adjust the distance and velocity scales by clicking on the values on the axis. At the top of the computer screen, click on "Analyze", and then "Examine". Now when you place the cursor at any point on the graph, a window will show you the value of the distance of the ball from the motion sensor at a specified time, and another small window will show you the value of the velocity of the ball at the same time. Play with this for a moment, checking different values at different positions. Now fill in the table by picking 4 positions during the motion where you can see speed is increasing as time goes by - for example, you might pick the positions x = 0.5, 0.9, 1.3, 1.7 m if these correspond to points where the speed is seen to increase on the velocity against time graph.

position/height (h) speed (v) Grav. Pot. Energy
(Ug=mgh)		 Kinetic Energy 
(K = 1/2 mv2)		 Total Energy 
(E = K + U)
         
         
         
         

In the space below draw a graph showing the kinetic energy, gravitational energy and total energy at the different heights from your table above.

Kinetic Energy Graph  

Rolling Cart

Set up a track so it is sloped at a reasonably large angle. Place the motion sensor at the top end of the track. Set it up so the zero end of the track is elevated, and the sensor is aligned with the scale on the track. You are to release a cart from x = 0.20 m on the track. 

1. What sort of energy does the cart have before it is released?

2. What sort of energy does the cart have when it is halfway to the end of the track?

Does it have more or less total energy than it had at the top before you released it?

3. What sort of energy does the cart have when it is just about to hit the end of the track?

Does it have more or less total energy than it had at the top before you released it?

Now, look at the data you collected for the cart. From this, you can find the speed of the cart at any position you like. We want the ground to be zero height, so to find the height for any position along the track you will have to measure it with a meter stick. (Measure it in METERS.)

On the screen, you will see two graphs, one showing the cart's position as time goes by, and another showing the cart's speed as time goes by. At the top of the computer screen, click on "Analyze", and then "Examine". Now when you place the cursor at any point on the graph, a window will show you the value of the distance of the cart from the motion sensor at a specified time, and another small window will show you the value of the velocity of the cart at the same time. Play with this for a moment. Now fill in the table by picking 4 positions during the motion where you can see speed is increasing as time goes by - for example, you might pick the positions x = 0.5, 0.9, 1.3, 1.7 m if these correspond to points where the speed is seen to increase. DON'T MOVE THE TRACK UNTIL YOU HAVE MEASURED THE HEIGHTS OF THE POSITIONS YOU HAVE CHOSEN.

position (x) speed (v) height (h) Grav pot. Energy
(Ug= mgh)		 Kinetic Energy
(K =1/2 mv2)		 Total Energy
(E = K + U)
           
           
           
           

In the space below draw a graph showing kinetic energy, gravitational energy and total energy as a function of height.

Kinetic Energy Graph  

Are your observations consistent with your thoughts about energy conservation? Explain.