Riding a Skateboard
The skateboarder is riding the half pipe.
Drag and release the skateboarder.
Notice the change in the skateboarder's velocity.
The bar chart on the left presents the skateboarder's kinetic energy (orange), potential energy (blue), and total energy.

Apply friction.
The skateboarder gradually decelerates (slows down) due to friction with the air, and his kinetic energy is converted into heat energy.

When the skateboarder comes to a halt, the simulation returns to its initial state and the skateboarder's energy totals zero.
Kinetic energy
Kinetic energy is the energy of a moving object. For instance, when a car travels, it has kinetic energy. The faster it goes, the higher its kinetic energy. When the car is stopped, it has no kinetic energy.
Potential energy
Potential energy is the energy an object gains when it is lifted to a higher place. For instance, when children climb the ladder of a slide, they gain potential energy. When they slide down, they lose the potential energy that they gained.
 

When we drag the skateboarder up the side of the half pipe, he gains potential energy.





When the skateboarder reaches maximum height, he stops for a moment, and again, like at the beginning, he has only potential energy and no kinetic energy.
When the skateboarder is in motion, potential energy turns into kinetic energy, which is then converted back into potential energy. At the end of each swing, however, the skateboarder ends up at the same height; in other words, he has the same potential energy each time.
If we measure the energy types during the entire experiment, we will find that the total amount of energy remains constant, as can be seen in the left-hand bar of the above graph. This is the Law of Conservation of Energy which states that energy neither disappears nor is created, but rather only changes from one form to another.
 

Will the skateboarder continue without stopping and without any effort?
That is indeed what happens in the above simulation, due to the conservation of energy. When the kinetic energy decreases, it turns into potential energy, which then turns back into kinetic energy.
In real-life there is friction between the skateboarder and the surface, and between the skateboarder and the surrounding air. This friction slows the skateboarder's motion and part of his kinetic energy converts into heat.
Over time, all of the energy the skateboarder had at the beginning of his ride will turn into heat and, if the skateboarder does not propel himself and add more kinetic energy to the system, he will eventually come to a halt at the bottom of the half pipe.
 

Answer the questions:
  1. The following 4 graphs describe the relative amounts of the different energy types in the simulation.
    Drag the appropriate picture of the skateboarder to each of the graphs.
 

  1. a. What is the maximum potential energy the skateboarder can gain in the simulation?
    1000 joules
    1700 joules
    2000 joules
    It is impossible to determine this from the simulation
    b. What is the maximum kinetic energy the skateboarder can gain in the simulation?
    1000 joules
    1700 joules
    2000 joules
    It is impossible to determine this from the simulation
    c. The skateboarder weighs 80 kg. What is the maximum height he can reach on the half pipe?
    1.70 meters
    2.20 meters
    2.60 meters
    3.50 meters

 

  1. Watch the skateboarders:
    a. Real skateboarders can ride their skateboards for long periods of time without slowing down, despite the friction that is created with the air.
    How do they do it?
    b. Does this contradict the Law of Conservation of Energy? Explain your answer.