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Force

12,711 views
Teacher/Instructor Matt Jones
Matt Jones

M.Ed., George Washington University
Dept. chair at a high school

Matt is currently the department chair at a high school in San Francisco. In his spare time, Matt enjoys spending time outdoors with his wife and two kids.

A force is defined in physics as anything that affects an object's acceleration. A force is a vector quantity because it has both magnitude and direction. The unit for force is the Newton (N) or kg/ms^2

Let's talk about force. Force is anything that causes an object to accelerate or decelerate okay Newton discovered this principle of force and he came up with his formula which is very widely used and you got to have to use this a lot to solve Physics problems okay. The formulas force equals mass times acceleration okay so what are the units for force? Well know the unit for mass is kilogram, the unit for acceleration is meters per second squared, so the unit for force is really unit of mass kilograms times meters per second squared okay. Now that's a lot to write and I don't want, have to keep witting that every time I'm writing a force so we can simplify that we can say one kilogram times meters over second squared equals 1 Newton so we're going to write a big N named after Sir Isaac Newton the man who discovered this.

We're talking about 1 kilogram times meters per seconds squared the mass times the acceleration. Okay there's a couple of different formulas you're going to need to use to solve problems and typically they'll ask you using this equation to give any 2 of these things solved for the third. So given a force and a mass solve for acceleration, given mass and acceleration solve for force, and so forth. So we can very easily move these around so we know that f equals m times a okay but if we want to solve for acceleration we can say okay well I want to get my m I want divide by m here divide by m here and I have the acceleration equals force divided by mass okay.

If I want to solve for mass I can again remove my a from this side by dividing and dividing and I get mass equals force divided by acceleration okay so let's look at some of the problems that you'd get typically with understanding Newton's laws of force okay. The first question might be what force is required to accelerate an object having a mass of 3 kilograms to an acceleration of 5 meters per second squared okay. So they've given us mass and they've given us acceleration so that's just a simple f equals m times a. And if I say 3 kilograms times 5 meters per second squared okay I get 15 kilograms times meters per second squared.

And again I don't like that unit so I'm just going to call that 15 Newton's okay pretty straight forward. Let's look at a second problem this time I'm going to ask something a little bit different okay. What is the mass of an object accelerated at 10 meters per second squared to a force of 75 Newton's okay? So now we want to know the mass okay so again and this time I'm saying m equals f divide by a okay and if I plug my numbers in here okay I've got my force is 75 Newton's which cancel the units we'll say is kilograms times meters per second squared okay. And my acceleration is 10 meters per second squared okay and now you can see that this unit cancels with that unit okay and I have 75 divided by 10 kilograms which equals 7.5 kilograms okay. So these are some of the ways we can apply this unit of force f equals ma to solve different types of problems.