Unit review time! Well, geez. Don't everybody don your party hats and blow into your noisemakers at once.
|Elementary and Middle School||4th Grade|
…Is that not how you usually relax? [Coop appears on the laptop]
Today it is!
Now without further ado... [Curtains reveal 'Unit Review']
….the unit review!
We'll start with energy. [Dino pointing at a blackboard]
As we know, energy is the ability of an object to do work…
…whether that's the kinetic energy of a moving ball… [Kid running away from a big ball]
…the electric energy that runs through electrical wires… [Engineer up a telegraph pole]
…or even the nuclear energy that keeps nuclear power plants going. [A nuclear power plant]
And of course, these kinds of energy are very different…
…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]
…unless you're playing a really intense game of catch….
One very important general form of energy is potential energy, which refers to the energy [Coop pointing at a blackboard]
possessed by an object.
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]
…or the chemical energy stored in all of the food we eat… [Guy eats a burger]
…or the gravitational energy in a roller coaster just before it's about to slide down [Roller coaster going up a steep climb]
and make us scream our heads off.
Which is one of the best kinds of potential energy.
Oh, and word to the wise?
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]
potential energy gets released in the process.
We also learned about energy transfer, aka how different forms of energy can transform
into new kinds.
For instance, when coal is burned, chemical energy becomes heat energy… [Coal burning]
…which turns water into steam, making kinetic energy… [Steam appears]
…which moves turbines, making more kinetic energy…
…which turns a generator, transforming this kinetic energy into electric energy… [Sparks come from the generator]
…which gets sent by wires all the way to your house to produce light energy. [Person sat by a light reading a book]
And sure, you could just read by the light of the burning coal, but where's the fun in
Another concept that came up was force: may it be with you. [Yoda next to a blackboard]
But outside of the Star Wars universe, force refers to a push or pull on an object.
This definition is pretty important in understanding Newton's three laws of motion. [Newton holding up his laws]
And since this is a review video, let's review what those are…
One: unless it's acted on by a force, an object will either not move at all…
…or continue moving at a constant velocity. [A wheel that is stopped and a wheel that is rolling]
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]
And last but not least, three: if one body applies a force to a second…
…that second body will exert a force of equal magnitude and opposite direction on
Sure, they're not as legally binding as traffic laws, but they're pretty much impossible to [Policeman stood by a stop sign]
The universe is slightly more powerful than a traffic cop. [The wheel runs into the traffic cop]
Next on our review list?
The concept of friction, which is when two objects rub against each other, causing the
objects to slow down.
So when you see a ball rolling to a stop, you're not seeing some sort of miraculous [Basketball stops rolling]
violation of Newton's first law.
You're just seeing friction!
The rubbing of the ball against the street exerts a force in the opposite direction of
the ball's movement, which gradually slows the ball down. [Football slowly comes to rest]
Unless you're still playing with that radioactive ball….then it might just burn a hole through [The radioactive ball melts into the floor]
the asphalt, or something…
And last but not least, we also learned the difference between mass and weight.
An object's mass is the quantity of matter it contains… [A block is shown with mass 100kg]
…while its weight is the force exerted on it by gravity.
That means if you go somewhere with a different gravitational pull, like the moon, your mass [The block on the moon]
will remain the same, but your weight will change.
Although traveling to space might be just a little bit more pricey than a gym membership… [Woman wearing a space hat holding dumbbells]
Review completed. [Guy in a hazmat suit appears on the great wall of China]
Now go do something fun!
Play catch, or something.
…Man, you're really into the whole "radioactive catch" thing, aren't you…? [Radioactive balls hits the other hazmat guy and knocks him over]
You do you.