EJC Physics H205 WEP 2023_1. Notes (FULL)

Content • Work • Energy conversion and conservation • Efficiency • Potential energy and kinetic energy • Power Learning Outcomes Candidates should be able to: (a) define and use work done by a force as the product of the force and displacement in the direction of the force (b) calculate the work done in a number of situations including the work done by a gas * which is expanding against a constant external pressure: W = pΔV (c) give examples of energy in different forms, its conversion and conservation, and apply the principle of energy conservation (d) show an appreciation for the implications of energy losses in practical devices and use the concept of efficiency to solve problems (e) derive, from the equations for uniformly accelerated motion in a straight line, the equation Ek = ½mv2 (f) recall and use the equation Ek = ½mv2 (g) distinguish between gravitational potential energy, electric potential energy^ and elastic potential energy (h) deduce that the elastic potential energy in a deformed material is related to the area under the force extension graph (i) show an understanding of and use the relationship between force and potential energy in a uniform field to solve problems (j) derive, from the definition of work done by a force, the equation Ep = mgh for gravitational potential energy changes near the Earth’s surface (k) recall and use the equation Ep = mgh for gravitational potential energy changes near the Earth’s surface (l) define power as work done per unit time and derive power as the product of a force and velocity in the direction of the force * Not required for 8867 H1 Physics, will be revised in greater details in H2 Topic 9: First Law of Thermodynamics ^ Will be dealt with in H2 Topic 13: Electric Fields Richard Feynman in 1961 said, “there is a fact, or if you wish, a law, governing all natural phenomena that are known to date . There is no known exception to this law —it is exact so far as we know. The law is called the conservation of energy. It states that there is a certain quantity, which we call energy that does not change in manifold changes which nature undergoes. That is a most abstract idea, because it is a mathematical principle; it says that there is a numerical quantity which does not change when something happens. It is not a description of a mechanism, or anything concrete; it is just a strange fact that we can calculate some number and when we finish watching nature go through her tricks and calculate the number again, it is the same.”

Sometimes, trying to analyse Physics scenarios using forces can be very complicated – there may be many forces or there are many interactions between various forces. Using the relationships between work, energy and power can be an alternative to deciphering the Physics. In Physics, work has a very specific meaning: As both force F and displacement s are vector quantities, the angle θ helps to manage the information concernin