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Energy, Work and Power

Energy, Work and Power. Aim: How do objects store and release energy?. Work. When a force moves an object, it is doing work. Work is measured in the joule (j) W = Fd Work only occurs when the force and movement are in the same direction. Work Example.

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Energy, Work and Power

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  1. Energy, Work and Power Aim: How do objects store and release energy?

  2. Work • When a force moves an object, it is doing work. • Work is measured in the joule (j) • W = Fd • Work only occurs when the force and movement are in the same direction

  3. Work Example • How much work is done while using a 50 N Force to hold a robot in place? • How much work is done by a robot pushing another robot back 5 m using a force of 100 N?

  4. Energy • Energy is the measure of a systems ability to do work. • Energy comes in many forms • Energy can not be created or destroyed, only converted from one type to another • There are many formulas for energy, depending on the type of energy we are concerned with

  5. Kinetic Energy • Kinetic energy is the energy that a moving object has. • The faster an object, the more kinetic energy it has. • The more massive an object, the more kinetic energy it has. • KE = ½ mass * velocity2 or ½ mv2 A 30kg robot is moving at 10 m/s. What is its kinetic energy?

  6. Open Note Quiz • You want to send a robot to Mars that will dig underground tunnels for future astronauts to live in. • Estimate the mass of the robot. • The robot needs an acceleration of 30 m/s/s. How much thrust force will be required? • Under that thrust, it moves 40,000 m before reaching escape velocity. How much work was done by the rockets? • The robot is now going 12000 m/s. What is its kinetic energy?

  7. Potential Energy • Potential energy is energy of an object due to its position or arrangement of the particles of a system. • Gravitational potential energy is mass*height*g • g ~ 10 m/s/s • There is also elastic, chemical and nuclear potential energy. • Potential energy can be converted into heat or kinetic energy.

  8. Conservation of Energy • Energy in a closed system is conserved. • Kinetic energy becomes potential energy and potential becomes kinetic. The total energy of a closed system is constant • What is a closed system? • Are robots a closed system?

  9. A little math • If energy is conserved, an object dropped from a height will change all its potential energy into kinetic. • It has mgh potential energy at the start so… • mgh = ½ mv2 • After doing algebra, you can see the velocity at the bottom will equal the square root of 2gh

  10. Power • Power is the rate at which work is done • The faster you want to do work, the more power is required • The formula is: power = work/time or • P = W/t

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