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Unit 2

Unit 2. Pages 248-249, 272-277, and 280-287. Gravity. Sir Isaac Newton Why do objects fall? A force pulls objects downward, towards the center of the Earth All objects are attracted to each other to some degree due to gravity. Mass. Amount of mass effects force of gravity

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Unit 2

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  1. Unit 2 Pages 248-249, 272-277, and 280-287

  2. Gravity • Sir Isaac Newton • Why do objects fall? • A force pulls objects downward, towards the center of the Earth • All objects are attracted to each other to some degree due to gravity

  3. Mass • Amount of mass effects force of gravity • Larger the mass, greater the gravitational force it exerts • An apple’s center is attracted to Earth’s center • Earth has more mass, so the apple moves and not Earth

  4. Distance • The force of gravity decreases as distance increases • Closer together the objects are, more force they exert on each other • Farther apart they are, the less force they exert

  5. Motion • Change in an object’s position • Speed = distance divided by time • Average speed = total distance divided by time • Velocity = involves speed and direction • Acceleration = change in velocity divided by time

  6. Speed • My dog runs 50 meters in 5 seconds. • What is my dog’s speed? • What are the units?

  7. Average Speed • It takes you 3 hours to travel 50 miles to Omaha. • What was your average speed? • What are your units in this problem? • What do we usually want our units of speed to be?

  8. Average vs. Instantaneous Speed • Average speed is how fast you traveled for the entire trip. • Instantaneous speed is how fast you are going at the moment that the police officer uses his radar gun on your vehicle and gives you a speeding ticket.

  9. Acceleration • My dog began his walk at 10 meters per second. 2 hours later, he was walking at 2 meters per second. • What was his acceleration? • What are the units?

  10. Momentum • Mass x velocity • Mass will be in grams, kg, mg, etc. • Velocity will be in meters per second • Conservation of Momentum = total momentum of system always stays the same

  11. Momentum • The 2000 kg truck is driving at 30 meters per second. • What is the truck’s momentum? • What are the units?

  12. Newton’s 1st Law of Motion • An object will remain at rest or move at a constant speed in a straight line unless acted upon by a force • Also known as the Law of Inertia • Inertia is the resistance to change in motion. • It is hard for en elephant to stop quickly because it has a lot of inertia carrying it forward.

  13. Newton’s 2nd Law of Motion • The force acting on an object is equal to mass of the object times the acceleration • Force = mass x acceleration • F= m x a • Mass must be in kilograms • Acceleration must be in m/s2

  14. Calculating Force • A 10 kg object accelerates at a rate of 45 m/s2. • Calculate its force. • What are the units? • A new unit you will use is Newtons! • 1 N = 1 kg x m/s2

  15. Newton’s 3rd Law of Motion • For every action force, there is an equal and opposite reaction • When a rocket is launched into space, its jets must first ignite its fuel pushing down against the ground. • This is the action. • The force of the explosion causes the rocket to fly upward. • This is the reaction.

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