![]() Because gravitational potential energy depends on relative position, we need a reference level at which to set the potential energy equal to 0. When it does positive work it increases the gravitational potential energy of the system. The force applied to the object is an external force, from outside the system. An object’s gravitational potential is due to its position relative to the surroundings within the Earth-object system. Why do we use the word “system”? Potential energy is a property of a system rather than of a single object-due to its physical position. For convenience, we refer to this as the PE g PE g gained by the object, recognizing that this is energy stored in the gravitational field of Earth. This energy is associated with the state of separation between two objects that attract each other by the gravitational force. We define this to be the gravitational potential energy ( PE g ) ( PE g ) put into (or gained by) the object-Earth system. ![]() The work done on the mass is then W = Fd = mgh W = Fd = mgh. If the object is lifted straight up at constant speed, then the force needed to lift it is equal to its weight mg mg. Let us calculate the work done in lifting an object of mass m m through a height h h, such as in Figure 7.5, near Earth's surface. The work done against the gravitational force goes into an important form of stored energy that we will explore in this section. When there is work, there is a transformation of energy. Show how knowledge of the potential energy as a function of position can be used to simplify calculations and explain physical phenomena.Ĭlimbing stairs and lifting objects is work in both the scientific and everyday sense-it is work done against the gravitational force.Show that the gravitational potential energy of an object of mass m m at height h h on Earth is given by PE g = mgh PE g = mgh. ![]() Explain gravitational potential energy in terms of work done against gravity.By the end of this section, you will be able to: ![]()
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