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Student Responsibilities

Student Responsibilities. Be willing and ready to learn When I am talking, you are not Do not hinder the learning of your classmates. Energy. What is Energy?. Energy is the ability to do work. What is Work?. Work is done when a force causes a change in distance. Work.

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Student Responsibilities

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  1. Student Responsibilities Be willing and ready to learn When I am talking, you are not Do not hinder the learning of your classmates

  2. Energy

  3. What is Energy? • Energy is the ability to do work. What is Work? • Work is done when a force causes a change in distance

  4. Work • Work can be expressed as an equation W = F d W – Work (Joules, J or Newton-meter, N m) F – Force (Newtons, N) d – Distance (meters, m)

  5. Sample Problem A man pushes a box across a floor with a force of 20 N for 10 m. How much work does the man exert?

  6. Work vs. Impulse • Impulse is a force exerted over an amount of time • Work is a force exerted over a distance • What about how much work is done over time?

  7. Power • Power is the rate at which work is done (how fast work is done) • Equation P = W t P – Power (Watts, W or Joules/second) W - Work (Joules, J or Newton-meter, N m) t – time (seconds)

  8. Horsepower • When the steam engine first came out, people wanted to know how they compared to horses. • James Watt expressed the power of his steam engines in horsepower, or the rate at which horses could do work. • 745 Watts = 1 Horsepower

  9. Sample Problems If a machine does 5000 J of work in 10 sec, what is the power?

  10. Energy Energy is the ability to do work Energy is measured in Joules When work is done, energy is used. Work, Power and Energy are scalar quantities

  11. Not Every Cat Hates Mice Nuclear Electrical Chemical Heat Mechanical Energy Comes in Different Forms!

  12. Potential Energy • Energy stored by an object because of its position or its condition • Gravitational Potential Energy • Energy stored as a result of its height.

  13. Gravitational Potential Energy PEgravity = mgh m – mass (kilograms) g – acceleration due to gravity (m/s2 ) h – height (meters) Note – Relationship between Work and PE

  14. Which has more PE?

  15. Sample Problem What is the PE of a 200 kg piano hoisted 10 meters above the ground?

  16. Elastic Potential Energy Elastic PE is found in a stretched or compressed elastic object (springs) If a spring is not stretched or compressed, then there is no elastic potential energy

  17. Kinetic Energy Kinetic Energy is the energy of motion Tells how much work is done to bring the object from rest to its present speed KE = ½ mv2 m – mass (kg) v – velocity (m/s) KE – Kinetic Energy (Joules)

  18. Sample Problem Find the K.E. of a 4.0 kg cart moving at 50 m/s.

  19. Conservation of Energy • Energy cannot be created or destroyed. It can be transformed from one form into another, but the total amount of energy never changes.

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