Note that h is positive when the final height is greater than the initial height, and vice versa. For example, if a 0. Note that the units of gravitational potential energy turn out to be joules, the same as for work and other forms of energy. As the clock runs, the mass is lowered. We can think of the mass as gradually giving up its 4. Figure 2.
See Figure 2. It is much easier to calculate mgh a simple multiplication than it is to calculate the work done along a complicated path. The idea of gravitational potential energy has the double advantage that it is very broadly applicable and it makes calculations easier.
From now on, we will consider that any change in vertical position h of a mass m is accompanied by a change in gravitational potential energy mgh , and we will avoid the equivalent but more difficult task of calculating work done by or against the gravitational force. Gravity is one of a small class of forces where the work done by or against the force depends only on the starting and ending points, not on the path between them. If he lands stiffly with his knee joints compressing by 0.
The initial PE g is transformed into KE as he falls. The work done by the floor reduces this kinetic energy to zero. The floor removes energy from the system, so it does negative work. Recalling that h is negative because the person fell down , the force on the knee joints is given by.
A much better way to cushion the shock is by bending the legs or rolling on the ground, increasing the time over which the force acts. A bending motion of 0. The kangaroo is the only large animal to use hopping for locomotion, but the shock in hopping is cushioned by the bending of its hind legs in each jump.
See Figure 3. Figure 3. The work done by the ground upon the kangaroo reduces its kinetic energy to zero as it lands.
However, by applying the force of the ground on the hind legs over a longer distance, the impact on the bones is reduced. Figure 4. The speed of a roller coaster increases as gravity pulls it downhill and is greatest at its lowest point. The roller coaster loses potential energy as it goes downhill. We neglect friction, so that the remaining force exerted by the track is the normal force, which is perpendicular to the direction of motion and does no work.
The net work on the roller coaster is then done by gravity alone. The loss of gravitational potential energy from moving downward through a distance h equals the gain in kinetic energy. Using the equations for PE g and KE, we can solve for the final speed v , which is the desired quantity.
This means that the final kinetic energy is the sum of the initial kinetic energy and the gravitational potential energy. Transferability Can be transferred between objects. Cannot be transferred between objects.
Measured from Place itself Bottom Environment-relative Relative to the environment of the object. Non-relative to the environment of the object. Equation 0. Simply put, the energy of motion is kinetic energy. The work required for accelerating the object of a certain mass, from the state of rest to motion. To speed up an object, we apply force, through which energy is transferred from one object to another, causing the object to move at a new and constant speed. The energy transferred is called kinetic energy, determined by speed and mass of the object, i.
The kinetic energy of an object, in motion, with a certain velocity, is same as the work performed on it. All the objects that are in motion or action, irrespective of horizontal or vertical motion, possess kinetic energy.
It is the energy which an object acquires, owing to its state of motion. For example, Falling of coconut, flowing of a river, moving of car or bus, etc. The different forms of kinetic energy are:. The term potential energy implies the energy which is stored in an object, at rest, as a consequence of its position relative to a zero position.
The energy is stored within the physical body, due to overcoming forces of nature. The unit of energy is Joules. It is a bit difficult to define energy in very precise terms because it is an abstract notion and not something tangible.
Energy is generally carried by something, usually in the form of movement. When objects move or remain in a position, they have energy which has different names. Though energy exists in various forms as mentioned earlier, it is important to understand that energy remains conserved always. When a form of energy is converted from one form to another during any process, the overall quantity of energy remains the same; there is no loss or gain.
This is what is called as conservation of energy. Our discussion here will focus on only two of the forms of energy — Potential Energy and Kinetic Energy. Let us now go into each of these separately to understand them first. An energy that is stored in an object and not moving, but which has the potential to move is called Potential Energy.
Potential Energy or PE as we can call is the energy possessed by an object because of its position relative to another body. The PE could also be the energy in a body due to its internal stress if any or the electrical charges in a body.
One of the most common forms of PE is the gravitational potential energy. The amount of PE, in this case, depends on the mass of the body. This is the energy required to move a body against the force of gravitation of the earth. A spring when extended has energy in it waiting to come back to its original position.
This also has enough potential energy. The term potential energy was first coined by a great physicist William Rankine in the 18 th century. Potential energy is always determined based on the position of a body and not based on its trajectory of movement. Some of the important factors that impact PE are its mass, its height relative to another object, and strength of the gravitational field.
Imagine a book or a ball of iron resting on a table at a height of 2 meters from the ground. If the same object were to be placed at a height of 10 meters from the ground, the object at the higher position will have a higher PE than the one at the lower height.
It is also called as restoring energy because this in a way forces the object to come back to its original energy state. When an object is raised from the ground, work is done against the gravitational force. Energy is spent in doing this work. When the object again falls to the ground, the object then gains energy from the gravitational energy.
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