What is the law of conservation of energy? Lesson link What is the law of conservation of energy?

Draw a line under last lesson’s work and write today’s title in your book... 04/12/2018 c/w Energy Transfers

Developing Explain what is meant by conservation of energy Learning Objectives Developing Explain what is meant by conservation of energy Securing Analyse the changes involved in the way energy is stored when a system changes Exceeding Explain that where there are energy changes in a closed system, there is no net change in the energy of that system

Engage For the following slides you need to draw a small diagram of the system and underneath explain the energy transfers involved System 1: A man pushes a boulder up a steep hill

Engage For the following slides you need to draw a small diagram of the system and underneath explain the energy transfers involved System 2: A car hits a wall

Engage For the following slides you need to draw a small diagram of the system and underneath explain the energy transfers involved System 3: A steam engine accelerating due to a constant force

Engage For the following slides you need to draw a small diagram of the system and underneath explain the energy transfers involved System 4: A motorbike slowing down

Engage For the following slides you need to draw a small diagram of the system and underneath explain the energy transfers involved System 5: A kettle boiling water

‘Lost’ Energy What does the law of conservation of energy state? Sometimes we might say some energy is ‘lost’. This isn’t particularly accurate however… What does the law of conservation of energy state? So what has actually happened to the ‘lost’ energy? When a mechanical process is occurring (e.g. like a human running or a motor spinning), there is commonly a rise in temperature. As such some of the energy provided (from the fuel) gets transferred into thermal/heat energy and sound!

Unwanted energy transfer Here is a perfect example of a system that has unwanted energy transfer. Some of the energy provided by the petrol (total energy) is being dissipated as heat energy which is the wasted energy The kinetic energy is what we actually want (to move the machine) so this is the useful energy What could we do to this machine to make sure that we waste less energy as heat?

Time to practice… Complete all the questions on the sheet provided. Make sure to write in full sentences. E.g. Question 1: State the law of conservation of energy Answer: The law of conservation of energy is….

Exam Practice 1a) State the equation linking gravitational potential energy, mass, g and height. (1 mark) (iii) A motor lifts a 130 g mass to a height of 63 cm. Calculate the gravitational potential energy (GPE) gained by the 130 g mass. (2 marks) (iv) Why is the amount of GPE gained by the mass less than the amount of electrical energy transferred to the motor? (2 marks) ....................................................................................................................................................................................................................................................................................

Exam Corrections: 1a) State the equation linking gravitational potential energy, mass, g and height. (1 mark) GPE = mass x g x height [1 mark] (iii) A motor lifts a 130 g mass to a height of 63 cm. Calculate the gravitational potential energy (GPE) gained by the 130 g mass. (2 marks) 130g = 0.13kg and 63cm= 0.63m [1 mark] GPE= m x g x h GPE= 0.13 x 10 x 0.63m = 0.819J [1 mark] (iv) Why might the amount of GPE gained by the mass be less than the amount of electrical energy transferred to the motor? (2 marks) .. Some of the energy provided to the motor will be used to overcome friction leading so some energy being wasted as heat and sound

Developing Explain what is meant by conservation of energy Learning Objectives Developing Explain what is meant by conservation of energy Securing Analyse the changes involved in the way energy is stored when a system changes Exceeding Explain that where there are energy changes in a closed system, there is no net change in the energy of that system

Independent Study Research and report on the methods used by motor companies to increase fuel efficiency (reduce dissipation of energy as heat) since 1975