Both kinetic energy and potential energy are proportional to the mass of the object. In a situation where KE = PE, we know that mgh = (1/2)mv2. If we divide and reorganize both sides by m, we get the relation 2gh = v2. Note that we can solve many problems when converting between KE and PE without knowing the mass of the object in question. Indeed, both kinetic energy and potential energy are proportional to the mass of the object. In a situation where KE = PE, we know that mgh = (1/2)mv2. Alternatively, the energy saving equation for v2 could be solved and KE2 calculated. Note that m could also be eliminated. [BL] [EL] Start by distinguishing mechanical energy from other forms of energy. Explain how the general definition of energy as the ability to work makes perfect sense in relation to the two forms of mechanical energy. Discuss the law of conservation of energy and clear up any misunderstandings related to this law, so the idea is that moving objects simply slow down naturally.

Identify the heat generated by friction as a common explanation for obvious violations of the law. [BL] Make sure there is a clear understanding of the distinction between kinetic energy and potential energy and between speed and acceleration. Explain that the word potential means that energy is available, but that does not mean that it should be used or that it is being used. See Figure 9.3. The amount of work required to lift the TV from point A to point B is equal to the amount of potential gravitational energy that the TV gains from its height above the ground. This usually applies to any object raised above the ground. When all the work done on an object is used to lift the object above the ground, the amount of work is equal to the object`s potential gravitational energy gain. However, keep in mind that due to the work done by friction, these transformations of energy work are never perfect.

Friction causes the loss of some useful energy. In the following discussions, we will use the approximation that transformations are smooth. As students pass through the lab, encourage lab partners to discuss their observations. Encourage them to discuss differences in outcomes between partners. Ask if there is confusion about the equations they use and if they seem valid based on what they have already learned about mechanical energy. Ask them to discuss the effect of drag and how density relates to this effect. Each side corresponds to the total mechanical energy. The expression in a closed system means that we assume that no energy is lost in the environment due to friction and air resistance. If we perform calculations on objects in free fall, this is a good hypothesis. For roller coasters, this assumption leads to a certain imprecision in the calculation. A 10 kg rock falls from a 20 m high cliff.

What is the kinetic and potential energy when the rock has fallen by 10 m? Now let`s look at the roller coaster in Figure 9.6. Work was done on the roller coaster to bring it to the top of the first elevation; At this point, roller coasters have potential gravitational energy. It moves slowly, so it also has a small amount of kinetic energy. When the car goes down the first slope, its PE is converted to KE. At the low point, much of the original PE has been converted into functionality, and the speed is at its maximum. As the car climbs the next slope, part of the KE is converted back into PE and the car slows down. [BL] Make it clear that energy is another property with units other than force or force. True or false – When a rock is thrown into the air, increasing the altitude would increase the kinetic energy of the rock, and then increasing the speed when it falls to the ground would increase its potential energy. Identify equivalent terms for stored energy and kinetic energy. In this activity, you calculate the potential energy of an object and predict the speed of the object when all that potential energy has been converted into kinetic energy.

You will then check your prediction. This simulation shows how kinetic and potential energy are related in a scenario similar to roller coasters. Observe the changes to the feature and EP by clicking on the fields in the bar chart. Also try the three skateparks of different shapes. Drag the skater onto the track to start the animation. Before showing the video, check all equations regarding kinetic and potential energy and energy conservation. Also, make sure students have a qualitative understanding of the ongoing energy transition. Refer to the Snap Lab and simulation lab.

This animation shows the transformations between function and pe and how the speed of the process varies. Later, we can go back to animation to see how friction converts some of the mechanical energy into heat and how total energy is preserved. We have already seen that mechanical energy can be potential or kinetic. In this section, we will see how energy is converted from one of these forms to the other. We will also see that in a closed system, the sum of these forms of energy remains constant. On a real roller coaster, there are many ups and downs, and each of them comes with transitions between kinetic energy and potential energy. Suppose no energy is lost due to friction. At any point in the journey, all the mechanical energy is the same and corresponds to the energy that the car had at the top of the first climb.