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[Dino and Coop singing]

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So by now, your head is probably chock-full of energy and motion facts. [Boys head opens and text books jump onto his brain]

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In fact, it's probably getting a little hard to remember all of the facts we've crammed [Plunger cramming the books into the boys head]

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into our brains.

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So just in case you've lost any along the way, let's sit back, relax, and do a unit review. [Boy sat on a beach, then a laptop appears]

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…Is that not how you usually relax? [Coop appears on the laptop]

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Well, whatever!

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Today it is!

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Now without further ado... [Curtains reveal 'Unit Review']

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….the unit review!

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We'll start with energy. [Dino pointing at a blackboard]

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As we know, energy is the ability of an object to do work…

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…whether that's the kinetic energy of a moving ball… [Kid running away from a big ball]

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…the electric energy that runs through electrical wires… [Engineer up a telegraph pole]

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…or even the nuclear energy that keeps nuclear power plants going. [A nuclear power plant]

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And of course, these kinds of energy are very different…

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…so you don't need to wear a hazmat suit to throw a ball around with your friends… [Two people in hazmat suits chucking a ball of toxic waste]

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…unless you're playing a really intense game of catch….

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One very important general form of energy is potential energy, which refers to the energy [Coop pointing at a blackboard]

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possessed by an object.

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There are lots of forms of potential energy, like the elastic energy stored in a bow that's [Guy pulls back a bow at an archery range]

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drawn tight…

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…or the chemical energy stored in all of the food we eat… [Guy eats a burger]

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…or the gravitational energy in a roller coaster just before it's about to slide down [Roller coaster going up a steep climb]

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and make us scream our heads off.

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Which is one of the best kinds of potential energy.

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Oh, and word to the wise?

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We don't recommend mixing roller coasters with archery and eating, no matter how much [Man on a roller coaster eating a burger and using a bow]

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potential energy gets released in the process.

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We also learned about energy transfer, aka how different forms of energy can transform

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into new kinds.

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For instance, when coal is burned, chemical energy becomes heat energy… [Coal burning]

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…which turns water into steam, making kinetic energy… [Steam appears]

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…which moves turbines, making more kinetic energy…

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…which turns a generator, transforming this kinetic energy into electric energy… [Sparks come from the generator]

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…which gets sent by wires all the way to your house to produce light energy. [Person sat by a light reading a book]

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And sure, you could just read by the light of the burning coal, but where's the fun in

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that?

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Another concept that came up was force: may it be with you. [Yoda next to a blackboard]

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But outside of the Star Wars universe, force refers to a push or pull on an object.

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This definition is pretty important in understanding Newton's three laws of motion. [Newton holding up his laws]

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And since this is a review video, let's review what those are…

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One: unless it's acted on by a force, an object will either not move at all…

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…or continue moving at a constant velocity. [A wheel that is stopped and a wheel that is rolling]

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Two: the total of all the forces on an object is equal to its mass times its acceleration. [Wheel on a scale and a car driving]

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And last but not least, three: if one body applies a force to a second…

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…that second body will exert a force of equal magnitude and opposite direction on

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the first.

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Sure, they're not as legally binding as traffic laws, but they're pretty much impossible to [Policeman stood by a stop sign]

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break.

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The universe is slightly more powerful than a traffic cop. [The wheel runs into the traffic cop]

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Next on our review list?

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The concept of friction, which is when two objects rub against each other, causing the

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objects to slow down.

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So when you see a ball rolling to a stop, you're not seeing some sort of miraculous [Basketball stops rolling]

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violation of Newton's first law.

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You're just seeing friction!

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The rubbing of the ball against the street exerts a force in the opposite direction of

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the ball's movement, which gradually slows the ball down. [Football slowly comes to rest]

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Unless you're still playing with that radioactive ball….then it might just burn a hole through [The radioactive ball melts into the floor]

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the asphalt, or something…

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And last but not least, we also learned the difference between mass and weight.

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An object's mass is the quantity of matter it contains… [A block is shown with mass 100kg]

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…while its weight is the force exerted on it by gravity.

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That means if you go somewhere with a different gravitational pull, like the moon, your mass [The block on the moon]

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will remain the same, but your weight will change.

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Although traveling to space might be just a little bit more pricey than a gym membership… [Woman wearing a space hat holding dumbbells]

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Tah-dah!

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Review completed. [Guy in a hazmat suit appears on the great wall of China]

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Now go do something fun!

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Play catch, or something.

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…Man, you're really into the whole "radioactive catch" thing, aren't you…? [Radioactive balls hits the other hazmat guy and knocks him over]

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You do you.

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