Transcript momentum
Newton's Laws of Motion Newton built upon the work of others... -1686, Sir Issac Newton publishes his book Principia in which he describes 3 laws relating forces to motion of objects -did not discover all 3 laws himself, but combined previous discoveries by other scientists and explained them in a way that people could understand -as a result, the 3 laws are commonly known as Newton's Laws of Motion Newton's First Law An object at rest remains at rest and an object in motion remains in motion at a constant speed and in a straight line unless acted on by an unbalanced force. -this law describes an object with a net force of zero acting on it EXPLAIN. -often referred to as the Law of Inertia (an object's resistance to any change in motion) WHAT IS THE LINK BETWEEN MASS AND INTERTIA? -this law is often difficult to observe because of friction WHY? Newton's Second Law The accelertion of an object depends on the mass of the object and the amount of force applied. -describes the motion of an object when an unbalanced force is acting on it EXPLAIN -acceleration decreases as mass increases & acceleration increases as mass decreases DOES THIS MAKE SENSE? -acceleration increases as force increases and acceleration decreases as force decreases HOW, THEN, ARE MASS AND FORCE RELATED TO ACCELERATION? Newton's Second Law expressed mathematically -Newton's second law can be expressed mathematically as a formula that shows the relationship between mass, force, and acceleration: acceleration = Force mass OR a= F m -it is often rearranged to look like this: Force = mass x acceleration OR F = m x a -either form can be used to solve problems as long as you know 2 of the variables EXAMPLES: 1. What is the acceleration of a 7 kg mass with a force of 68.6 N moving it toward the Earth? (1 N = 1 kg x 1m/s/s) 2. What force is needed to accelerate a 1,250 kg car at a rate of 40 m/s/s? 3. What is the mass of an object if a force of 34 N produces an acceleration of 4 m/s/s? Newton's Third Law Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first. HOW IS THIS LAW COMMONLY PHRASED? -describes how all forces act in pairs -the interaction of force pairs affects the motion of objects -action force is the initial force exerted on an object -reaction force is the force exerted back from the object IS IT POSSIBLE FOR FORCE PAIRS TO ACT ON THE SAME OBJECT? WHY? -effect of reaction force (especially on falling objects) can be difficult to see USE NEWTON'S 2ND LAW TO EXPLAIN WHY THIS IS SO. Examples of force pairs The bat exerts a force on the ball, sending it toward the outfield. The ball exerts an equal force on the bat in the opposite direction, but the bat doesn't fly backwards because the batter is exerting another force on it. The air inside the balloon exerts an outward force, while the air outside the balloon exerts and equal force inward. The bowling ball exerts a force on the pin, pushing it to the left. At the same time, the pin exerts an equal force on the ball, pushing it to the right. CAN YOU THINK OF SOME OTHER FORCE PAIRS? WHY IS IT THAT THE PIN FALLS DOWN, BUT THE BOWLING BALL CONTINUES TO ROLL? THE BALL HAS MOMENTUM. Momentum -momentum is a property of a moving object that depends on the object's mass and velocity -an object with a large mass or high velocity, or both has greater momentum than an object with a small mass or low velocity or both -the more momentum an object has, the harder it is to stop it, or make it change direction -momentum can be calculated using the following formula: momentum(p) = mass(m) x velocity(v) EX: 1. What is the momentum of a 15,000 kg semi traveling at a constant velocity of 30 m/s? 2. What is the momentum of a 1,300 kg car traveling at that same velocity? WHAT DO YOU THINK WILL HAPPEN IF THESE 2 VEHICLES WERE TO COLLIDE? (YOUR ANSWER SHOULD BE SCIENTIFIC!) Momentum is Conserved -when a moving object hits another object, momentum is transferred to the other object -it may be all or only some of the momentum that is transferred -if it is only some, the rest of the momentum stays with the first object -this is why the bowling ball continues to roll after hitting the pin and is called The law of conservation of momentum -any time two or more objects interact, they may exchange momentum, but the total amount of momentum stays the same NAME SOME MORE EXAMPLES OF THIS LAW. HOW DOES NEWTON'S THIRD LAW HELP TO EXPLAIN CONSERVATION OF MOMENTUM.