Do Now: What are Newton’s 3 Laws of Motion? http://science.discovery.com/interactives/literacy/newton/media/newto nfinal415.swf
So what do the laws tell us? Looking at the second law we get Newton ’ s famous equation for force: F=ma m is equal to the mass of the object and a is the acceleration ***Units of force are Newtons A Newton is the force required to give a mass of one kilogram and acceleration of one metre per second squared (1N=1 kg m/s 2 ) Examples: 1. What net force is required to accelerate a car at a rate of 2 m/s 2 if the car has a mass of 3,000 kg? F=_______ m=______ a= __________ 2. A10 kg bowling ball would require what force to accelerate down an alleyway at a rate of 3 m/s 2 ? F=______ m=______ a=______
So what do the laws tell us? However, a person standing still is still being accelerated Gravity is an acceleration that constantly acts on you F=mg where g is the acceleration due to gravity
So what do the laws tell us? Looking at the third law of motion “ for every action, there is a equal and opposite reaction ” So what does this mean? Consider the following diagram A box with a force due to gravity
So what do the laws tell us? “ for every action, there is an equal and opposite reaction ” A force is being exerted on the ground from the weight of the box. Therefore the ground must also be exerting a force on the box equal to the weight of the box This is called the normal force or F N
Equilibrium The object is stationary, therefore all the forces must add up to zero. Forces in the vertical direction: F N and F g There are no horizontal forces How would you define the term equilibrium?
What is force? How do we measure it? A force is a push or a pull on an object. Arrows called vectors show a force’s Magnitude (strength) Direction
How to find net force To find net force: If the forces are opposing, find the difference between them. 4N 2N What is the net force? If the forces are parallel, add them. 4N 4N What is the net force?
Balanced and Unbalanced Forces If the net force is zero, the forces are balanced and no change in speed or direction will occur. 3N 3N If the net force is greater than zero, the forces are unbalanced and the speed or direction will change in the direction of the net force. 3N 5N