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CEFR 레벨
난이도
자막 (381 세그먼트)
- This is a mousetrap car.
(funky music)
They're coming for competitions in high school
physics classes, just like the egg drop challenge
or building toothpick bridges.
The goal is to build a car that travels the furthest
or goes the fastest, but in either case, the only power
provided to move the car is from a single mouse trap.
So today I'm gonna show you how to win first place
by building some cars with the world record holder.
And then we're gonna go to the West Coast championships to
see all these principles in action.
And, don't leave.
I know that 99.7% of you have never nor will ever make one
of these, but I will break down in simple terms how
I know this car will go twice as far as this one
and then I'll prove it
and then we'll discuss why
you see these DVD wheels so often.
But do they work and why do some winning cars have
wheels that look like this?
But before we fly all the way out to Texas to
meet the world record holder, I need to lay the foundation
for the one overarching fundamental physics principle
behind the mousetrap car.
It's called mechanical advantage.
And to do that, I'm gonna need my niece and nephews.
I'm gonna bet you guys I could lift my car off the ground
using just my pinkies.
If I can't do it, can have this crisp Benjamin,
but if I can you, guys have to grab me ice cream.
All right, deal?
- I said nothing else but your pinkies.
- I am just using my pinkies.
- No, just your pinkies.
- That's what I'm doing.
This is really good you guys.
Thank you.
If you're willing to move a greater distance
you're able to reduce the amount
of force by a proportional amount.
I can't lift 500 pounds worth of car one time
but I could lift 10 pounds 50 times.
A mechanical advantage is the ratio
of the output force over the input force.
So in this case it's 50.
That means my hand had to travel 50 times further
than just lifting the car in one shot
but the weight was 50 times less
so it was totally worth it.
This principle of mechanical advantage is everywhere.
Let's take a look at a few examples.
If I have four pulleys, that means I have to pull the rope
down four times further than the dumbbell goes up.
But in exchange, it feels four times lighter.
So this has a mechanical advantage of four.
For the ramp, you look
at the ratio of the length to the height.
Your mechanical advantage therefore is 2.2.
That means I have to travel a little further
but the brick should feel 2.2 times lighter pulling
up the ramp versus just pulling the brick straight up.
And sure enough, if you measure each with a scale
this is exactly what you see.
If you think about it
a screw is just a ramp wrapped around a nail.
So here you look at this as traveled
around the thread and divide by the space in
between the threads to get a mechanical advantage of nine.
And as you know, if you really wanna multiply your force
use a ratchet wrench.
Now the distance your hand travels
for one full rotation is 300 times longer than the distance
the screw moves vertically between one thread.
The total mechanical advantage is 300.
It's like a really long short ramp.
So if this scale reads six pounds
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