Hi! I'm Matt. I'm going to tell you the story of how I learned physics.
One day, I decided to visit my friend who lives in an apartment building downtown.
I was going up in the elevator when I started to think " Isn't it so weird that I'm going up even though I'm not moving? I wonder how much force it takes to move me..."
So when I got to my friend's house, I asked her about it!
Hey Sarah! You're good at physics right? When I'm going up in an elevator, how much force do you think it takes to move me up?
Well actually, you can calculate that! All you need to do is use Newtons laws!
Newton? What's a Newton?
Newton was an old scientist who was sitting under a tree one day when an apple fell on his head. That's how he discovered gravity. He also made a bunch of physics laws, and had a unit of force named after him.
Cool! But... how does that help us solve the elevator problem?
Well, two of Newton's laws are Fg=mg and Fnet=ma, and those formulas will help us calculate the force of the elevator on you
Let me explain. An elevator by itself needs force to move itself up. A person, by themselves does not move, but they have a force of gravity pushing them down.
So overall, the elevator has to exert a much larger force, because it not only needs the force to move up, but it also needs a force to overcome gravity.
I see.
So to find that force, you need to add the original force of the elevator, and a force equal and opposite to gravity, and that'll give you the answer.
So first lets calculate the force of gravity using Fg=mg. Fg represents the force of gravity, m represents mass, and g represents the value of gravitational acceleration, which is -9.8m/s^2. How much do you weigh?
I weigh 100kg, I think.
So using the formula, it would be Fg= (100kg)(-9.8m/s^2), which gives you -980 newtons. So if the elevator needs to overcome gravity, then it would be the same amount of force, but in the opposite direction. So it would be 980N.
Yeah! So Fnet means the net force, which in this case is the force of the elevator moving upwards, and a means acceleration. In order to solve this problem, we need to know how fast the elevator accelerates... where could we find that...
Cool! So I guess now we calculate the force of the elevator moving up, using Fnet=ma, right?
Over here on the elevator! It's 5m/s^2. Which means that the net force is 5m/s^2*100kg, which is 500N!
This elevator accelerates at 5m/s^2
So that means that the force the elevator is exerting on me is... 500N+980N... which is.... 1480N! Wow! I just did physics!
Yeah! You did!
Yes! So in that case, since there's no force to move it, the only force it's exerting is overcoming gravity to prevent you from falling. So it would be exerting 980N!
Hm... so what about when the elevator is standing still? Is it exerting any force on me then?
Well, the elevator isn't moving at all, and it's not preventing gravity from acting on you since you're falling...so... it's not exerting any force at all!
What about... if the elevator cord breaks and I'm freefalling in the elevator?!
This one will surely stump her...
Wow! Cool! Well thanks for helping me!
Any time! I hope you learned something about physics today!
The End
Sukurta daugiau nei 30 milijonų siužetinių lentelių