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Active Physics Talk Section 8

LAW OF CONSERVATION OF ENERGY. Active Physics Talk Section 8. Investigate Recap. #1: What caused the penny to go up into the air? What did you have to do to make sure it went almost up to the ceiling without hitting it?

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Active Physics Talk Section 8

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  1. LAW OF CONSERVATION OF ENERGY Active Physics Talk Section 8

  2. Investigate Recap • #1: What caused the penny to go up into the air? • What did you have to do to make sure it went almost up to the ceiling without hitting it? • #3-5: What happened to the deflection as the ball was rolled from a higher distance? • #6-9: What happened as you increased the deflection of the ruler from 2 cm to 6 cm?

  3. Law of Conservation of Energy • A force can change the position and speed of an object in a way that allows the position and speed to change back to how it was originally • What allows for this?

  4. Vocabulary Law of Conservation of Energy – energy cannot be created or destroyed; it can be transformed from one form to another, but the total amount of energy remains constant Kinetic Energy – energy associated with motion; KE = ½ mv2 Potential Energy – energy associated with position Gravitational Potential Energy – the energy an object possesses because of its vertical position from Earth; GPE = mgh Elastic Potential Energy – the energy of a spring due to its compression or stretch; EPE = ½ kx2

  5. Law of Conservation of Energy • In Case You Missed it: ENERGY CANNOT BE CREATED OR DESTROYED! IT IS TRANSFORMED FROM ONE FORM TO ANOTHER! • Total Energy = Kinetic Energy + Potential Energy

  6. Energy and Work • Review: What must happen in order for an acceleration to occur?

  7. Vocabulary Work – the product of the displacement and the force in the direction of the displacement; W=Fd Law of Conservation of Energy – energy cannot be created or destroyed; it can be transformed from one form to another, but the total amount of energy remains constant Kinetic Energy – energy associated with motion; KE = ½ mv2 Potential Energy – energy associated with position Gravitational Potential Energy – the energy an object possesses because of its vertical position from Earth; GPE = mgh Elastic Potential Energy – the energy of a spring due to its compression or stretch; EPE = ½ kx2

  8. Equations Work: W=Fd; W = Work (N•m), F = Force (N), d = distance (m) Elastic Potential Energy: EPE = ½kx2; EPE = Elastic Potential Energy (N•m), k = spring constant (N/m), x = amount of bending (m) Gravitational Potential Energy:GPE = mgh; GPE = Gravitational Potential Energy (N•m), m = mass (kg), g = acceleration due to gravity (m/s2), h = height through which object is lifted (m) Kinetic Energy:KE = ½mv2; KE = Kinetic Energy (N•m), m = mass (kg), v = speed (m/s) Newton: kg•m/s2 N•m = Joule (J)

  9. Energy and Work • One way to think about energy is to consider it as “stored work”

  10. Conservation of Energy in the Pole Vault • Let’s try to identify the different kinds of energy • Coin Toss • After you bent the ruler, but before you let it go: • After you let it go (rising), and before it hits the ground (falling): • At the peak (the highest the coin will go up before it starts to come back down; hint: v = 0 m/s)

  11. Conservation of Energy in the Pole Vault • Let’s try to identify the different kinds of energy • Pole Vault • While the pole vaulter is running • When the pole vaulter uses the pole to spring herself up (bends pole) • When the pole vaulter is in the air and rising • When the pole vaulter is no longer rising, but has not started falling yet • When the pole vaulter is falling down

  12. Richard Feynman’s Explanation of the Conservation of Energy • Child has 28 blocks (possibly in the middle of the floor in her bedroom) • Sometimes one or two blocks are elsewhere (mom and dad’s room, living room), but there are still 28 blocks total

  13. PRACTICE! • A weightlifter uses a force of 325 N to lift a set of weights 2.00 m off the ground. How much work did the weightlifter do? • Want • Given • Formula • Solve (units)

  14. PRACTICE! • How much energy is stored in a pole with a spring constant of 15 N/m if it is deflected 1.6 m? • Want • Given • Formula • Solve (units)

  15. PRACTICE! • One of the highest pop flies every recorded in baseball was about 172 m. What is the gravitational potential energy of a baseball with a mass of 145 g that is hit that high into the air (g = 10 m/s2)? • Want • Given • Formula • Solve (units)

  16. PRACTICE! • A football player has a mass of 100.0 kg and runs at a speed of 6.0 m/s. What is his kinetic energy? • Want • Given • Formula • Solve (units)

  17. What Do You Think Now? • If champion pole vaulters can clear a 6.0 m high bar with a 5.5 m long pole, why can’t they vault over a 12 m high bar with a pole 11.0 m long? • What factors (variables) do you think limit the height a pole vaulter has been able to attain?

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