Natural Sciences Grade 7 Term 3 Energy and

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Natural Sciences Grade 7 Term 3: Energy and Change Potential and kinetic energy

Topic 2 Potential and Kinetic Energy Law of conservation of energy Natural Sciences - Grade 7

Law of conservation of energy • Energy cannot be created or destroyed, but it is changed or converted from one form to another. • Energy flows / transfers between different parts of a system. • We can study this transfer of energy within a system through flow diagrams. Natural Sciences - Grade 7

Flow diagram example: • Plastic Ruler The ruler bends. The bent ruler has elastic potential energy. The potential energy changes to kinetic energy when the bent ruler is released. NB: When drawing an energy flow diagram you need to identify: v Where the energy comes from (the input energy). v Where the energy goes ( transfer into output energy). v The changes in potential and kinetic energy in the process. Natural Sciences - Grade 7

Flow diagram example: Water wheel Gravity lets the water fall onto the fins of the water wheel. Gravitational potential Energy is changed to kinetic energy. The water at a height, has gravitational potential energy. A person has to wind up the toy car. It now has elastic potential energy. The elastic potential energy is now changed to kinetic energy. Wind up toy car [above] Natural Sciences - Grade 7 The falling water causes the water wheel to turn. The toy car moves.

Flow diagram example: Electrical toy car [example] Cells have potential energy. Circuit is closed an electric current starts to flow. The electric current flows and turns the motor. Natural Sciences - Grade 7 The electric motor turns the wheels and the car moves [kinetic energy]

Flow diagram of the energy system of a boy eating a banana. Banana [potential energy]. Boy eats the banana. Energy is stored in the boy’s muscles. Natural Sciences - Grade 7 The boy runs [kinetic energy].