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Transcript
HAPPY VALENTINE’S DAY! Please get your folders. Copy down tonight’s homework. Have last night’s homework on your desk (conclusions for Part 2 of Shipping and Sliding; graph do-over) Today, we will: Talk about Newton’s other two laws 1. What did the boy cat say to the girl cat on Valentine’s Day? 2. What did the boy octopus say to the girl octopus? 3. What did the boy light bulb say to the girl light bulb? 4. What did the paper clip say to the magnet? 5. What do you call a very small valentine? Tomorrow’s quiz motion graphs definition of force Newton’s three laws of motion Objects accelerate in the direction of the net force applied to objects. FORCE = MASS ● ACCELERATION acceleration = force mass To a scientist, acceleration is any change in velocity. OK, so remind me: What is VELOCITY??? Velocity is speed in a given direction. So, how can velocity change??? The object can SPEED UP. The object can SLOW DOWN. The object can CHANGE DIRECTION. A dog chasing its tail is accelerating – WHY? The only way to NOT accelerate is to... Travel in a straight line at constant speed. (all lines are straight) acceleration = force mass •The SI unit for force is the Newton. •Let’s say a 4N force acts on a 2kg mass. What is the acceleration? •What if we increase the force to 8N? •What if we increase the mass to 4kg? LET’S GO SHOPPING! acceleration = force mass •The more force that is applied, the more the object will accelerate •(putter vs. feather) •The greater the mass of the object, the less it will be accelerated by a given force •(golf ball vs. ping pong ball) WHAT THIS MEANS: 1. To get something to accelerate more (speed up quickly, slow down quickly, change direction quickly), you must apply more force. Example: slamming on the brakes to stop quickly WHAT THIS MEANS: 2. It takes more force to accelerate a bigger thing than a smaller thing. For every action force, there is an equal and opposite reaction force. According to Newton, whenever objects A and B interact with each other, they exert forces upon each other. When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body. There are two forces resulting from this interaction – the force you exert on the chair and the force the chair exerts on your body. These two forces are called action and reaction forces. This means that when I am pushing on the wall, THE WALL IS PUSHING BACK ON ME!!! Action-reaction force pairs make it possible for objects to move. What is the direction of your force when you are walking forward? What is the direction of your force when you jump on a trampoline? Think about the direction of the force you apply when you row a boat: Think about the direction of the force you apply when you shoot an arrow. The bat and ball each put a force on each other – each also experiences a reaction force. This sends the ball back out toward the field and sends the bat backward (recoil). The reaction of a rocket is an application of the third law of motion. Various fuels are burned in the engine, producing hot gases. The hot gases push against the inside tube of the rocket and escape out the bottom of the tube. As the gases move downward, the rocket moves in the opposite direction. How do you get something to accelerate a lot? Give an example of an action/reaction force pair in this classroom. How does the Coke/Mentos car illustrate the 1st Law? 2nd Law? 3rd Law?