![]() You also have to look up the mass of a neutron.ĭon’t forget to convert km into m to do these calculations, although, to save space, we omitted showing these conversions. ![]() To answer these questions, you can use the definition of kinetic energy in Equation 7.6. ![]() What is the kinetic energy of such a particle? What was its mass? (c) In nuclear reactors, thermal neutrons, traveling at about 2.2 km/s, play an important role. (a) What is the kinetic energy of an 80-kg athlete, running at 10 m/s? (b) The Chicxulub crater in Yucatan, one of the largest existing impact craters on Earth, is thought to have been created by an asteroid, traveling atĢ2 km/s and releasing 4.2 × 10 23 J 4.2 × 10 23 J of kinetic energy upon impact. Since objects (or systems) of interest vary in complexity, we first define the kinetic energy of a particle with mass m. At speeds comparable to the speed of light, the special theory of relativity requires a different expression for the kinetic energy of a particle, as discussed in Relativity. Note that when we say “classical,” we mean non-relativistic, that is, at speeds much less that the speed of light. 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.Besides, some of the concepts to be developed in this module will be useful in understanding the succeeding topics, like when students learn about the common characteristics of waves and when they relate these to the characteristics of sound and light waves.By the end of this section, you will be able to: Motion is considered to be the first topic because it is the most concrete manifestation of the abstract concept of energy. Electrical energy is described as an energy that is transferred by moving electrical charges through a complete circuit. Sound and light are introduced as forms of energy that are transferred by waves while heat is introduced as an energy that is transferred either by randomly moving particles, or by electromagnetic waves (radiation). In this grade level, the focus is on the sources of the different forms of energy and the different ways by which they are transferred from one place to another. All these forms belong to kinetic energy they are all associated with some kind of motion-the motion of waves, electrons, atoms, molecules, and objects. Among the many forms of energy, motion, heat, light, sound, and electrical energy are the most common and most familiar among students. At the end of the quarter, students should be able to realize that energy exists in different forms, energy transfers from one body to another, and that motion is the concrete manifestation that a body possesses energy. Overview The topics covered in Grade 7 deal with the relationship between motion and energy.
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