Lab Objectives:

Learn about conservation of energy with a skater dude! Build tracks, ramps and jumps for the skater. view the kinetic energy, potential energy and thermal energy (due to friction) as the scatter moves. Experience the differences in kinetic potential and thermal energies at different planets or even at space.

Introduction:

            The law of conservation of energy states that the total amount of energy in an isolated system remains constant. As a consequence of this law, we can say that energy neither created nor destroyed, but can change its form.

The total energy E of a system (the sum of its mechanical energy and its internal energies, including thermal energy) can change only by amounts of energy that are transferred to or from the system. If work W is done on the system, then

W = DE = DEmech + DEth + DEint

If the system is isolated (W = 0), this gives

DEmech + DEth + DEint = 0

The skate park is an excellent example of the conservation of energy. For the isolated skate-track-Earth system, the law of conservation of energy equation has the form

DEmech + DEth = 0

Mechanical Energy: The mechanical energy Emech of a system is the sum of its kinetic energy K and its potential energy U:  Emech = K + U

The conservation of mechanical energy can be written as

DEmech = DK + DU = 0. It can also rewritten as  K1 + U1 = K2 + U2

In which the subscript refer to different instants during an energy transfer process.

Gravitational Potential Energy: The potential energy associated with a system consisting of Earth and a nearby particle is gravitational potential energy. If the particle moves from y1 to height y2 , the change in gravitational potential energy of the particle-Earth system is

DU = mg(y2 – y1)=mgDy

Kinetic Energy: The kinetic energy is associated with the state of motion of an object. If an object changes its speed from v1 to v2 , the change in kinetic energy is

 DK = K2 – K1 = ½ mv22 – ½ mv12

Simulation: Open Energy Skate Park

http://phet.colorado.edu/simulations/sims.php?sim=Energy_Skate_Park

Take some time familiarize yourself with the skater and his track. It helps you to practice with the following features and controls.

Track selector: click on Tracks and select from the drop down menu. For example, the “Double well (Roller Coaster)” shown above.

Reset: This rests the simulation to default values and sets the track to friction parabola track.

Skater selector: clicking on Choose skater… will allows you to choose a skateboarder with a different mass.

Measuring Tape: Check the Measuring Tape Box when you want to make measurements. Drag the left end of the tape measure to where you start your measurement, and then drag the right end to the final location. To make a reference horizontal line to your measurement, check the potential energy reference box and drag the blue line you see on the screen to the initial position.

Graph Selector: If you would like to observe graphs that depicts the relationships among potential, kinetic, and thermal energy of the simulation, click buttons under the Energy Graphs. The types of graphs are shown above. You can also add pie graph by checking the show pie chart box. These graphs can be shown with or without the Thermal energy.

Gravity: you may change the gravitational force by changing the location or the sliding bar underneath Gravity box.

Additional Features: Clicking the Clear Heat makes the track frictionless. You can also edit the track friction and the skater mass using Track friction and Edit Skater buttons. You can also control the speed of the skater using the slide bar under the screen.