# AP Physics 1: 1.2 Object Interaction and Forces

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.

AP Physics 1 | Object Interaction and Forces |

Language | English Language |

Science Practice 2 | Using math appropriately |

### Transcript

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

elephant's kinetic energy larger than the tigers kinetic energy

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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]

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

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

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]

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