8.3 Moving About Focus 3: Energy and Work

Outcomes 26. Define the law of conservation of energy 27. Identify that a moving object possesses kinetic energy and that work done on that object can increase that energy 28. Solve problems and analyse information to determine the kinetic energy of a vehicle and the work done using the formulae E k = ½mv 2 and W = Fs 29. Describe the energy transformations that occur in collisions 30. Analyse information to trace the energy transfers and transformation in collisions leading to irreversible distortions

Two Useful Formulae E k = ½mv 2 W = Fs ▫Ek = kinetic energy in Joules ▫m = mass in kilograms ▫v = velocity in ms-1 ▫W = work in Joules ▫F = force in Newtons ▫s = displacement in m Work can be done on an object in order to increase its kinetic energy. When this happens, F s = 1/2mv 2 Note – “s” for displacement rather than “r”

Law of Conservation of Energy Energy cannot be created or destroyed, only changed in form. Energy can be … ▫transferred from one object to another.  e.g.: a hot cup of coffee warming your hands. ▫Transformed from one form to another  e.g.: chemical potential energy in a battery changing into light energy in a light globe.

Types of Collision Elastic collision: all the kinetic energy from the first vehicle is either still “in” the first vehicle or has been transferred to the second vehicle. Inelastic collision: some of the kinetic energy from the first vehicle is transformed into other forms of energy. ▫Examples of the other forms of energy include heat, sound, light and elastic potential energy in the crumpled part of the car.

Energy transfers and transformations in collisions leading to irreversible distortions kinetic energy sound energy heat energy elastic potential energy “crash, bang!!” in the “crumple zone” sparks, friction If two cars collide, some of the kinetic energy of the first car will be transferred to the second car