yego.me
💡 Stop wasting time. Read Youtube instead of watch. Download Chrome Extension

Force, mass and acceleration | Movement and forces | Middle school physics | Khan Academy


3m read
·Nov 10, 2024

So, I have three different asteroids over here, and they have different masses. We'll talk a lot more about what mass means, but one way to think about it is how much stuff there is there. There are other ways to think about it.

Let's say that this first asteroid is twice the mass of either of these two smaller ones, and these two smaller ones have the same mass. Now, we've attached the back of a rocket to each of these asteroids. In fact, this one over here has two rockets, and we're going to assume that all of the rockets are equivalent, and we ignite them all. So, they all exert the same force each on the asteroid.

For example, we have a net force acting leftward on this large asteroid. We have the same net force acting on this smaller asteroid, also going to the left. On this other smaller asteroid, we have two times that net force acting to the left. So, what I want you to do is pause this video and think about which of these asteroids is going to be accelerated the most and which of these asteroids is going to be accelerated the least.

Alright, so you might have an intuition that the larger the force, the more acceleration you might see. So, let me write it like this: you might get a sense that if you increase your force, that's also going to increase your acceleration. It does turn out that that is indeed the case.

Now, the other notion that you might have is that the more of the stuff that there is, the more mass that you have, the harder it is to accelerate it. So, if your mass is larger, then your acceleration is lower. It turns out that these things are all proportional. For example, if we just compare these two masses right over here, they have the same net force acting on them.

I keep saying net force; that means you just net out all of the forces acting in a certain dimension. For example, if I had another identical rocket acting in the opposite direction, they would net out, and this asteroid right over here wouldn't be accelerated at all. But going back to our example here, we have the same net force acting on each of these asteroids, but the first asteroid has twice the mass of the second asteroid.

So, how do you think the accelerations will relate? Well, as you might imagine, the acceleration on the larger asteroid is going to be half the acceleration on this asteroid. Or another way to think about it, this asteroid is going to have twice the acceleration as this first asteroid, and that's because it has half the mass.

One way you can relate force, mass, and acceleration—and this is one of the most important equations in all of physics—is that force is going to be equal to mass times acceleration. Or I could say the magnitude of the force is equal to the mass times the magnitude of the acceleration.

So notice in this example right over here, our forces are the same, but the masses are different. If I have half the mass as I have over here, I'm going to have twice the acceleration. That might make intuitive sense if you've ever tried to apply the same force to something that has a small mass versus something that has a large mass.

Now, if we compare these two asteroids, they have the same mass here, but the force here, the net force acting in that left direction, is double. So, if you double the force but don't change the mass, then you're going to have twice the acceleration. This is going to have twice the acceleration of this one, and this one's going to have twice the acceleration of that one.

But the important thing to realize is how force, mass, and acceleration are connected.

More Articles

View All
Is Success Luck or Hard Work?
During the COVID lockdown, this headline went viral: “Nearly half of men say they do most of the homeschooling… …three percent of women agree.” I bring this up not to debate who’s right, but because it’s a great example of something called egocentric bias…
2015 AP Chemistry free response 3e | Chemistry | Khan Academy
The initial pH and the equivalence point are plotted on the graph below. Accurately sketch the titration curve on the graph below. Mark the position of the half equivalence point on the curve with an X. All right, so we have— they show us the initial pH …
Brave New Words - Bill Gates & Sal Khan
Hi everyone, it’s here from Khan Academy, and as some of you all know, I have released my second book, Brave New Words, about the future of AI, education, and work. It’s available wherever you might buy your books. But as part of the research for that boo…
Be Like Sal: 3 Ways a Tablet Can Energize Your Digital Teaching!
Thank you so much for joining today or this evening, depending on where you’re calling from. This is Jeremy Schieffen at Khan Academy, and I’m so excited they’re joining with us because if anything at Khan Academy, 2020 has been the year of the tablet. We…
Rule of 70 to approximate population doubling time | AP Environmental Science | Khan Academy
When we’re dealing with population growth rates, an interesting question is how long would it take for a given rate for the population to double. So we’re going to think about doubling time now. If you were to actually calculate it precisely, mathematica…
How to Analyze an Income Statement Like a Hedge Fund Analyst
Being able to understand and analyze a company’s income statement is one of the most foundational pieces of being a great investor. If you want to invest successfully, this is one of the most important skills in helping you make money by investing. In thi…