Transcript 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 • 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 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 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 Speed • My dog runs 50 meters in 5 seconds. • What is my dog’s speed? • What are the units? 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? 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. 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? 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 Momentum • The 2000 kg truck is driving at 30 meters per second. • What is the truck’s momentum? • What are the units? 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. 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 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 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.