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Warm Up 9/24

Warm Up 9/24. Directions: Write which of Newton’s Laws these sentences describe: I can move the small snowball I made for the snowman’s head, but I will need help moving his belly. When I push back with my ski poles, I move forward. The harder I pull, the faster my dog runs.

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Warm Up 9/24

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  1. Warm Up 9/24 Directions: Write which of Newton’s Laws these sentences describe: • I can move the small snowball I made for the snowman’s head, but I will need help moving his belly. • When I push back with my ski poles, I move forward. • The harder I pull, the faster my dog runs.

  2. Potential Energy is stored energy. Ex. A stretched rubber band has the potential or ability to fly across the room. Potential Energy

  3. 1. Gravitational Potential Energy 2. Chemical: This type of energy is stored when you eat food or burn an object 3. Electrical: Used to power houses (also found in batteries) 4. Elastic: Stored when you stretch a rubber band (earthquakes too) 5. Nuclear: Produced by splitting the nucleus of an atom. Types of Potential Energy

  4. A long way down… How would you describe a high diver? As someone who is: • brave • insane • full of beans • full of gravitational potential energy (GPE). GPE is the amount of energy an object has because of its position above the ground, i.e. its height.

  5. What is gravitational potential energy? The gravitational potential energy (GPE) of an object on Earth depends on its mass and its height above the Earth’s surface. • When a bungee jumper starts to fall, he starts to lose GPE. • As the elastic cord pulls the bungee jumper back up, he gains GPE.

  6. GPE = mass x gravitational field strength x height How is GPE calculated? The GPE of an object can be calculated using this equation: • Mass is measured in kilograms (kg). • Gravitational field strength is measured in newtons per kilogram (N/kg), usually taken as 10N/kg (9.8) on Earth. • Height is measured in meters (m). • GPE is measured in joules (j).

  7. Factors affecting GPE

  8. Calculating GPE question 1 An eagle with a mass of2kg flies at a height of200m above the ground. How much gravitational potential energy does the eagle have? GPE = mass x gravitational field strength x height = 2 x 10 x 200 = 4,000J

  9. changein height GPElost = mass x gravitational field strength x Calculating GPE question 2 An apple with a mass of 200g falls 3m from its branch to the ground. How much GPE will the apple have lost when it reaches the ground? = 0.2 x 10 x 3 = 6J

  10. GPE, mass and height calculations

  11. What is kinetic energy? The word ‘kinetic’ comes from the Greek word ‘kinesis’, meaning motion. Kinetic energy is the energy an object has because it is moving. All moving things have kinetic energy, but the amount of energy they have is not just dependent on how fast they are moving. What other factors affect the kinetic energy of a moving object?

  12. Kinetic Energy

  13. Kinetic Energy

  14. KE = ½ x mass x velocity2 = ½mv2 How is kinetic energy calculated? The kinetic energy (KE) of an object can be calculated using this equation: • Mass is measured in kilograms (kg). • Velocity is measured in meters per second (m/s). • KE is measured in joules (j).

  15. Calculating kinetic energy question A truck with a mass of 1,500kg travels at a velocity of 20m/s. What is the kinetic energy of the truck? kinetic energy = ½ xmass x velocity2 = ½ x 1,500 x 202 = 300,000J = 300kJ

  16. KE = ½mv2 Ö 2KE m 2KE v2 v = m = Rearranging the KE equation Sometimes it is necessary to rearrange the kinetic energy equation in order to calculate the mass or the velocity of a moving object. What are the rearranged versions of this equation for calculating mass and velocity?

  17. KE, mass and velocity calculations

  18. Too much kinetic energy Doubling the mass of a moving object doubles its kinetic energy, but doubling the velocity quadruples its kinetic energy. If the velocity of a car is slightly above the speed limit, its kinetic energy is much greater than it would be at the speed limit. This means that: • It is more difficult to stop the car and there is more chance of an accident. • It the car does collide with something, more energy will be transferred, causing more damage.

  19. The kinetic energy of cars

  20. 1,000kg 2,000kg 20mph 40mph Dangerous speeding? Use the KE = ½mv2 equation to fill in the kinetic energy values in the table below for two cars each traveling at two different velocities. KE = 40kJ KE = 80kJ KE = 160kJ KE = 320kJ What factor – mass or velocity – has the greatest effect on the kinetic energy of a moving object?

  21. Feeling energetic? Who has the most kinetic energy: Rita or the cat?

  22. Ö 2KE mass velocity = Ö 2 x 2,250,000 20,000 = Calculating velocity question A truck has a mass of 20,000kg. If its kinetic energy is 2.25mJ, at what velocity is it travelling? KE = ½ xmass x velocity2 = 15m/s

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