Newton’s LawsAn Instructional Slideshow by George Souﬂis
Newton’s First The puck, as with all objects, Law tends to move at a constant speed and in a straight line. After you hit In this picture the hockey puck the puck it is moving entirely bydemonstrates Newton’s ﬁrst law as it this tendency that we call inertia.moves across the smooth, !ictionless table. The puck would move inﬁnitely on its straight path at this speed, but it hits the table’s edge.
So to review...• Objects (like the hockey puck) tend to do what they’re already doing, and this is called inertia.• If something is moving North at 5 miles per hour, it’s going to continue going North at 5 miles per hour...• ...UNLESS
In these next pictures we see a The skateboarder is moving at a skateboarder riding along a smooth, ﬂat constant speed in a straight line by road. When the skateboarder hits the his own inertia. In other words, rock, it demonstrates the second part there is no force continuing the of the First Law. skateboard’s motion. The rock hitting the skateboard, therefore, exerts a force that is unbalanced. This stops the skateboard’s path down the road.The rock hitting the skateboard exerts a force that is unbalanced - since there is no force moving the skateboard. The skateboarder,however, has not had a force to stop it, and will continue forward at the skateboard’s original velocity.
To Sum It All Up...• Newton’s First Law deals with an object’s tendency to keep doing what it’s already doing (inertia)• An object can change what it’s doing when an unbalanced force acts on it.
Newton’sSecond Law In this next picture we can see the Second Lawat work. If the two rocks are pulled with equal force, the rock with less mass will have more acceleration. For the rocks to accelerateequally, the more massive rock must have a larger force acted on it.
Here we see anotherexample of the Second Law. To be accelerated (as when being tackled), a massivefootball player needs a large force acting on it. In same way, a less massive football player with high acceleration also exerts a large force.
To Sum It All Up...• To generate the same acceleration, more massive objects require more force.• The same force can be generated by a less massive object with more acceleration and a more massive object with less acceleration.
Newton’s Third Law In this picture we can see Newton’s Third Law. The diver pushes down on the diving board. At the sametime the diving board pushes up on the diver. In this way, all forces work in pairs.
In this picture we can see another example of the Third Law. As the man uses the paddle to push water backwards, the canoe movesforward. This is because of the pair of forces that act on thepaddle. In this way it is clear tosee that the pairs of forces areboth opposite in direction and equal in magnitude.
To Sum It All Up...• All forces come in pairs that are equal and opposite.