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AP Physics 1 Videos 86 videos

AP Physics 1: 2.5 Changes and Conservation Law
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AP Physics 1: 1.2 Object Interaction and Forces 213 Views


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Description:

The real moral of the story here is just "don't get in the way of elephants or tigers." That is not the kind of kinetic energy you want to absorb.

Language:
English Language

Transcript

00:02

here's your shmoop du' jour brought to you by elephants sure they [elephants by a small lake]

00:06

have good memories can distinguish between human languages and can

00:09

communicate with each other but ask one of them to calculate kinetic energy and [woman asking elephants to calculate kinetic energy]

00:14

see how far that gets you yeah an elephant and tiger are racing through

00:18

the Serengeti National Park hoping to find some water the elephant weighs 12 [Elephant and tiger running through Serengeti]

00:22

times as much as the tiger but the tiger runs twice as fast by what factor is the

00:28

elephant's kinetic energy larger than the tigers kinetic energy

00:33

[muttering] all right what to do what to do well

00:39

wait a second we've got a handy little equation to calculate kinetic energy [boy thinking about how to solve the problem]

00:42

it's even called the kinetic energy equation here it is kinetic energy

00:47

equals one-half mass times velocity squared all right now we're not really

00:51

[boy studying on a computer screen] doing any math here we're just trying to figure out how changing some parts of

00:55

this equation alter the results in fact let's start off by having a kinetic

01:00

energy equation for the tiger and the elephant and setting them equal to each

01:04

other and since the numbers don't really matter we're just going to make the mass [kinetic energy equation for elephant and tiger]

01:08

one and the velocity one for each of these majestic beasts in fact let's get

01:14

rid of that whole one-half part of the equation too we don't need it not having

01:18

actual numbers or units is kind of freaking us out right now but it's fine [woman screaming and tearing her hair]

01:21

its fine.. we can deal with it so at this point both of these equations equal one

01:26

that's what one times one squared comes out to now Ellee the elephant has 12

01:32

times the mass of the tiger so we'll change that in her equation so if we

01:37

stopped right here we'd find that our long-term trend has 12 times the kinetic [elephants walking together]

01:41

energy of the stripy guy but the elephant is slower than the big feline

01:46

in fact she's running half as fast in this quest for water so let's change [elephants travelling together slowly]

01:51

that 1 squared to 1/2 squared well 1/2 squared equals 1/4 so now if we do the

01:57

math I multiply 12 times 1/4 we'll find that the elephant has 3 times the

02:02

kinetic energy that's it answer C is correct if you came up with answer B, 6

02:07

you might have forgotten to square the velocity multiplied it and if you chose [schoolboy frustrated and smashes his laptop]

02:11

A, 24 you might have thought the elephant running twice as fast as a tiger but

02:15

really it's the other way around and if you chose D 72 well we all make a mistake [a boy wearing his shoes as gloves and pants on top of his head]

02:21

sometimes so now if you're ever on the plains of Africa and you see a tiger in

02:25

an elephant in a hurry to a watering hole you'll know how to think about their

02:28

differences in kinetic energy just make sure you're doing this from a safe [man with white hair and a lab coat studying the tiger and the elephant]

02:32

distance you wouldn't want to get in the way of either one of these guys [man in a lab coat trampled by elephant]

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