Transcript of Newton's Laws of Motion

by the 17th century the Enlightenment or Renaissance was taking root across Europe and the emergence in astronomy from the dark days of the geocentric universe was being replaced with the heliocentric universe first introduced by Nicholas Copernicus then shown geometrically by Johannes Kepler and then finally proven observational ii by galileo a young scholar by the name of Isaac Newton in England at the time was studying natural philosophy at the University of Cambridge and he spent much of his time thinking about motion and in order to discuss Isaac Newton's laws of motion let's just clarify a few common terms associated with motion so here we have a car it's going down the highway if we say that the car has a specific speed let's say 60 miles per hour that's the same thing as saying that it's covering some distance over an amount of time but the velocity on the other hand is a little bit different it's speed combined with a direction so 60 miles per hour northbound however you want to define that direction you've got to include some direction component to convert speed into velocity likewise acceleration is just a change in velocity so we can imagine ourselves pressing down on the accelerator pedal that'll increase our speed therefore we've accelerated but we can also do the same thing just by slowing down we're decreasing our speed so technically that's a form of acceleration as well finally we can even change our velocity or rather we can accelerate by keeping our speed the same but just turning the steering wheel just making a turn left or right while keeping the speed the same is acceleration as well why because acceleration is a change in velocity and velocity is simply speed combined with the direction so this brings us to Newton's first law of motion it states that any object that is at rest or is in a state of continuous motion is going to remain that way unless some force acts upon it so this is often called the law of inertia so in this image we have the Apollo 14 service and command module and you notice that there's a rocket engine on the back of the spacecraft and it's not burning and yet the spacecraft is heading along its way toward the moon the reason for this is because inertia once the spaceship got up to speed that rocket engine cut off and it was allowed to Coast all the way to the moon if it were to miss the moon it would continue to coast and keep on coasting and nothing would stop it unless there was some kind of a force that would act upon it but the second law states that an acceleration on a body is proportional to and in the direction of the force acting upon it we often write that mathematically as force is the product of mass times acceleration if you'd like you could turn it around and say that acceleration is the same thing as the force divided by a mass so here we have an astronaut holding in her hand a telephone booth size instrument that was going to be installed on the Hubble Space Telescope it's very heavy that is to say it's very massive and in order for her to move it she has to exert some kind of a force so if you take a look at that second equation at the bottom we have acceleration is equal to the force divided by the mass if the mass is very very large then the force needs to be rather large in order to generate an acceleration likewise if the mass is very small then a small force is all that is needed to achieve the same acceleration Newton's third law is often misstated as for every action there's an equal and opposite reaction but it's more accurately stated as a result of forces so for every force there is always an equal reaction force but it's in the opposite direction so here we have SpaceX's Falcon heavy rocket on its inaugural flight as it flies off the launch pad it throws fuel out the back end the rocket exhausts fuel in one direction and the fuel pushes back on the rocket in the opposite direct with the exact same amount of force this causes the rocket to accelerate we learned that from Newton's second law right if you have a mass the rocket has a mass you give it a force it accelerates well you throw the fuel out the back the fuel pushes back on you and therefore you accelerate in the opposite direction so those are Newton's three laws of motion and we're now going to show how they apply to create things like gravity