We can do the same thing for a few other forces, and we will see that this leads to a formal definition of the law of conservation of energy. One can study the conversion of gravitational potential energy into kinetic energy in this experiment. On a smooth, level surface, use a ruler of the kind that has a groove running along its length and a book to make an incline see Figure 5.
Place a marble at the cm position on the ruler and let it roll down the ruler. When it hits the level surface, measure the time it takes to roll one meter. Now place the marble at the cm and the cm positions and again measure the times it takes to roll 1 m on the level surface.
Find the velocity of the marble on the level surface for all three positions. Plot velocity squared versus the distance traveled by the marble. What is the shape of each plot?
Figure 5. A marble rolls down a ruler, and its speed on the level surface is measured. Figure 6. Hydroelectric facility credit: Denis Belevich, Wikimedia Commons.
Figure 7. A toy car moves up a sloped track. That is, the energy stored in the lake is approximately half that in a 9-megaton fusion bomb. Skip to main content. Work, Energy, and Energy Resources. Search for:. Gravitational Potential Energy Learning Objectives By the end of this section, you will be able to: Explain gravitational potential energy in terms of work done against gravity. Show how knowledge of the potential energy as a function of position can be used to simplify calculations and explain physical phenomena.
Example 1. The Force to Stop Falling A Potential energy is essentially what it sounds like, though there are a few intricacies involved. The actual potential energy of an object depends on its position relative to other objects.
For example, a brick has more potential energy suspended off of a two-story building than it does resting on the ground. That's because the brick's relative position to the Earth gives it more energy. Two bricks next to each other don't give each other more energy though, because there is no force acting on them.
The same principle can be applied on any scale, be it galactic or atomic. Indeed, atoms possess potential energy as well, though their constant movement shifts much of their potential energy into kinetic energy. Also notice how much energy the moving car has. No wonder accidents can cause so much damage! At least one of the values you entered is incorrect. Try again. The correct values have been entered. At least one of the values you entered had an incorrect number of significant figures.
The two examples above illustrate the two forms of potential energy to be discussed in this course - gravitational potential energy and elastic potential energy.
Gravitational potential energy is the energy stored in an object as the result of its vertical position or height. The energy is stored as the result of the gravitational attraction of the Earth for the object.
The gravitational potential energy of the massive ball of a demolition machine is dependent on two variables - the mass of the ball and the height to which it is raised. There is a direct relation between gravitational potential energy and the mass of an object. More massive objects have greater gravitational potential energy. There is also a direct relation between gravitational potential energy and the height of an object. The higher that an object is elevated, the greater the gravitational potential energy.
These relationships are expressed by the following equation:. In the above equation, m represents the mass of the object, h represents the height of the object and g represents the gravitational field strength 9. To determine the gravitational potential energy of an object, a zero height position must first be arbitrarily assigned. Typically, the ground is considered to be a position of zero height. But this is merely an arbitrarily assigned position that most people agree upon.
Since many of our labs are done on tabletops, it is often customary to assign the tabletop to be the zero height position. Again this is merely arbitrary.
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