With this history in mind, we can now state the classical definition of kinetic energy. (If you have ever played billiards or croquet, or seen a model of Newton’s Cradle, you have observed this type of collision.) The idea behind this quantity was related to the forces acting on a body and was referred to as “the energy of motion.” Later on, during the eighteenth century, the name kinetic energy was given to energy of motion. The first body stops, and the second body moves off with the initial velocity of the first body. At the end of the seventeenth century, a quantity was introduced into mechanics to explain collisions between two perfectly elastic bodies, in which one body makes a head-on collision with an identical body at rest. This does not depend on the direction of the velocity, only its magnitude. It’s plausible to suppose that the greater the velocity of a body, the greater effect it could have on other bodies. Evaluate the kinetic energy of a body, relative to different frames of reference.Calculate the kinetic energy of a particle given its mass and its velocity or momentum.The average car is able to convert only about 20% of the energy in the fuel into useful motion.By the end of this section, you will be able to: Our automobiles are even less efficient than our bodies at converting energy. The energy content of food is found by carefully burning the food item in a device known as a calorimeter and measuring the amount of heat generated. If we tried to warm up water by burning a peanut, we would find that a portion of the energy would be wasted warming the air and the container. When we eat a peanut, our body only converts about 25% of the energy in the peanut into usable energy for our body – the rest is lost along the way. Whenever energy is converted from one form to another, it loses some energy along the way. The peanut, if converted into electrical energy, would power a smartphone (screen on) for about 3 hours. How much energy is that? If the body was 100% efficient, it would be enough energy for a 65 kg person to climb to the top of a 25-storey building! It would also be enough energy (if you burned the peanut) to raise the temperature of 1 litre of water by 14☌. How much energy could we get from one peanut? The average peanut weighs about 2.5 grams and contains about 60 kilojoules (14 calories) of energy. The energy from the Sun is translated into chemical energy and stored inside the seeds for the next generation of peanuts.Ī peanut could also transfer its energy to a person who eats it. The plant eventually matures, blooms and produces more peanuts. The plant eventually tunnels its way up and out of the soil into the light and forms leaves so that it can begin to collect energy from the Sun and absorb nutrients from the soil. When soil conditions are right, the tiny embryo (nub at the end of a peanut) begins to grow using the stored energy in the rest of the seed to begin plant development. If we look at how a peanut grows, a peanut plant begins life as a planted peanut. A peanut as energy transferĪ peanut is a much more complex example of energy transfer. These small energy losses will eventually stop the pendulum, and it will come to rest at position B. Also, because of its speed in swinging through the air, the air would be moving, and some of the kinetic energy of the pendulum would have been transferred to the air. If we measure very carefully, we would find that the bending of the string where it is tied at the top would have become slightly warmer because of the fibres of the string rubbing together. If the pendulum could regain all of its original height it would swing forever, but there are small energy losses along the way.
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