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Kids learn about the science behind friction including how it works as a force to slow things down, how it helps us stand, preventing friction, types, and fun facts.

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Kids learn about the science behind gravity, the mysterious force of planet earth including why it is important, what is weight, and fun facts. What is gravity?

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Kids learn about force in the science of physics and the laws of motion including units and measurement. How to calculate force from mass and acceleration.

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What would happen if you tried to slide across the cement in your tennis shoes? You probably wouldn't move much and you might even trip, right? What if you tried to slide across a wooden floor wearing only socks? Or slide across a sheet of ice in your boots? You'd probably slide right along. Why is it easier to slide across ice or a wooden floor than cement? The answer is (drumroll, please): FRICTION. Friction is a force that holds back movement of an object - in this case, you. The rougher a surface, the more friction.The smoother a surface, the less friction.
Fun Facts

Liquid smooths out a surface, creating less friction. For example, it's harder for a car to stop on a wet road than a dry one because the water creates a barrier between the car and the road. The tires don't have as much contact with the road.

Oil in a car engine lubricates the parts so they experience less friction. Friction causes heat, which can damage a car engine.

When one object rubs or slides against another, it slows down. The energy is changed from moving (kinetic) energy to heat energy. When you rub your hands together, for example, your hands get warm.

Vocabulary

1. Friction: The resistance that occurs when two objects move against each other.

2. Barrier: Something that prevents movement.

3. Lubrication: To apply an oily substance to reduce friction.

Question and Answer
Question: Can we predict how much friction will occur between two objects?
Answer: Yes. Several things determine how much friction there is. First, the rougher something is the more friction it will create. Try rubbing your hand over sandpaper. It's hard to do, right? Now rub your hand over a piece of smooth paper. Less friction! How much force is used also determines friction. If you push hard on your bike pedals, you create more friction - and slow down more quickly - than if you press lightly. The weight - or mass - of an object also determines friction. Try blowing a feather across a table. Easy, right? Now try blowing a rock of the same size across the table. The rock has more mass, which creates more friction and makes it harder to move.

Learn More
Head over to Mocomi to watch a short video about friction.

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What would happen if you tried to slide across the cement in your tennis shoes? You probably wouldn't move much and you might even trip, right? What if you tried to slide across a wooden floor wearing only socks? Or slide across a sheet of ice in your boots?

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What is Friction in Physics? - Science for Kids | Educational Videos by Mocomi

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Force, Work and Energy | #aumsum #kids #science #education #children

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Interesting Gravity Facts - Acceleration, G-Force, Mass, Formula, Law, Orbit

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Enjoy our range of interesting gravity facts that help explain how gravity relates to both life on Earth and other objects in our solar system. Learn about important concepts such as acceleration, mass, tides and orbits as well as some useful formulas, strange trivia and other fun information relating to the topic of gravity.

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Friction is a force that holds back the movement of a sliding object. That's it. Friction is just that simple.

You will find friction everywhere that objects come into contact with each other. The force acts in the opposite direction to the way an object wants to slide. If a car needs to stop at a stop sign, it slows because of the friction between the brakes and the wheels. If you run down the sidewalk and stop quickly, you can stop because of the friction between your shoes and the cement.

What happens if you run down the sidewalk and you try to stop on a puddle? Friction is still there, but the liquid makes the surfaces smoother and the friction a lot less. Less friction means it is harder to stop. The low friction thing happens to cars when it rains. That's why there are often so many accidents. Even though the friction of the brakes is still there, the brakes may be wet, and the wheels are not in as much contact with the ground. Cars hydroplane when they go too fast on puddles of water.

Friction only happens with solid objects, but you do get resistance to motion in both liquids and gases. This doesn't involve sliding surfaces like friction does, but is instead the kind of resistance you get if you try to push your way through a crowd. It's a colliding situation, not a sliding one. If the gas is air, this is referred to as air resistance.

If you were in the space shuttle and re-entering the atmosphere, the bottom of the shuttle would be getting very hot. The collisions that occur between the molecules of the air being compressed by the shuttle, heat up the air AND the shuttle itself. The temperature on the top of the shuttle is also warm, but nowhere near the temperatures found on the bottom.

Although liquids offer resistance to objects moving through them, they also smooth surfaces and reduce friction. Liquids tend to get thinner (less viscous) as they are heated. Yes, that's like the viscosity of the oil you put in your car. Car engines have a lot of moving parts, and they rub on each other. The rubbing produces friction and the result is heat. When oil is added to a car engine, the oil sticks to surfaces, and helps to decrease the amount of friction and wear on the parts of the engine. An engine that runs hotter requires a more viscous oil in order for it to stick to the surfaces properly.

Measures of friction are based on the type of materials that are in contact. Concrete on concrete has a very high coefficient of friction. That coefficient is a measure of how easily one object moves in relationship to another. When you have a high coefficient of friction, you have a lot of friction between the materials. Concrete on concrete has a very high coefficient, and Teflon on most things has a very low coefficient. Teflon is used on surfaces where we don't want things to stick; such as pots and pans.

Scientists have discovered that there is even less friction in your joints than in Teflon! It is one more example at how efficient living organisms can be.

Or search the sites for a specific topic.

Space Shuttle Thermal Protection (NASA-eClips Video)

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Friction is a force that holds back the movement of a sliding object. That's it. Friction is just that simple. You will find friction everywhere that objects come into contact with each other. The force acts in the opposite direction to the way an object wants to slide.

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Gravity is the force that keeps us from floating off into space. It literally keeps our feet on the ground! We feel the effects of gravity every second of our lives (unless we're astronauts), but most of us don't give it a second thought. This article sets out to explain gravity for kids - and anyone else who has ever wondered why they fall down, rather than up.

(See more Science Articles.)

Before we get started, here's a question:
If I had a 1kg weight in one hand, and a 100g weight in the other hand, and dropped them at exactly the same time, which would fall the fastest and therefore land first?
You'll find the answer lower down the page!

Gravity For Kids: Introduction

Let's start at the beginning.

If you drop a stone, it falls to the floor. Why is this?

Everyone knows that the answer is 'Gravity'!
But what is gravity? It's more than just a word!
The real answer is that a force - a force we call gravity - is acting on the stone, and pulling it towards the Earth.

Gravity is, quite simply, a force of attraction between objects. The stone is 'attracted' to - pulled towards - the Earth.

Thanks to Isaac Newton, we know that:
The more mass an object has, the bigger the force of attraction.
And ...
The closer something is, the bigger the force of attraction.
The Earth, having a very large mass, and being very close, exerts a strong pull on anything in its vicinity, including:

a stone when you drop it,

your body when you fall over,

and something large and round flying above your head ...

... The moon!
But why doesn't the moon come crashing into the Earth? And why didn't Neil Armstrong come falling towards the Earth when he took his 'small step for a man'?
We'll get to that. But first we're going to take a look at how we came to understand gravity.

The Discovery of Gravity

Back to the question from the top of the page:
If I had a 1kg weight in one hand, and a 100g weight in the other hand, and dropped them at exactly the same time, which would fall the fastest ... and therefore land first?
The answer (which I hope you got right) is that they would both fall at the same speed (or, more specifically, with the same acceleration), and both would hit the ground at the same time.

Don't worry if you got it wrong. Even Aristotle (who lived from 384 to 322 BC) believed that heavier objects fall faster than lighter objects, so you're in good company!

In fact, most people believed this until around 1638, when Italian astronomer Galileo Galilei proved that objects fall at the same speed - whatever their weight (or, strictly speaking, their mass. See this article to find out the difference).

Note: An astronomer is someone who studies 'celestial bodies', such as moons, stars, planets, comets and galaxies.

Another note: We refer to Galileo Galilei by his first name, for the very good reason that that was how he referred to himself, as was the custom in Italy at the time.

The story goes that Galileo proved his theory by dropping different-sized balls from the leaning tower of Pisa.

He found that the speed at which an object falls is determined not by how heavy it is, but by how long it has been falling.

Galileo's Experiment Repeated ... On The Moon!

In 1971 astronaut Dave Scott performed a similar experiment to Galileo's. Not from the leaning tower of Pisa, but on the moon. Scott dropped a feather and a hammer, and - surprise, surprise -both reached the surface of the moon at the same time.

Galileo calculated the rate at which objects accelerate while falling to Earth. That rate is now known to be 9.81 m/s² - although this figure changes slightly depending on whereabouts on Earth it is measured.

The figure also ignores the effects of air resistance and any other factors which may create anything other than a perfect, frictionless fall.

Galileo increased our understanding of gravity, but even he couldn't explain why it was that things fell to the ground in the first place.

Isaac Newton

It was up to Englishman Isaac Newton - arguably the greatest scientist who ever lived - to realise what gravity actually was.

Like all scientists, Newton used the work of other scientists as a basis for his own theories.

German astronomer Johannes Kepler had worked out the rotation of the planets round the sun (using observations made by Danish astronomer Tycho Brahe).

Using Kepler's laws of planetary motion, Newton realised that gravity was a force of attraction, and the size of the force depended both on the mass of the objects involved, and the distance they were from each other.

Newton's Law Of Universal Gravitation

Newton's law of universal gravitation, published in 1687 states that 'any two bodies in the universe attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them'.

The law can be written as an equation:

F = G ((m1xm2) / r²).

The force (F) between two objects of masses m1 and m2 is equal to the product of their masses divided by the square of the distance (r) between them.
G is the gravitational constant. It remains the same wherever it is applied in the Universe.
Using Newton's laws, we can find out why two objects of different mass fall with the same acceleration.

Basically, if the mass of an object is doubled, the gravitational force is doubled, but the rate of acceleration remains the same.

If the mass of an object is halved, then the gravitational force is halved, but again the rate of acceleration remains the same.

Using Maths to Find Planets

Using Newton's Law Of Universal Gravitation, scientists were able to calculate the presence of Neptune before it was 'properly' discovered.

In the 1820s it was found that Uranus (then the most distant discovered planet) was not where Newton's laws suggested it should be.

Over the next decades, astronomers in England and France independently concluded that Uranus's movement was being affected by another, unknown, planet, and calculated where this other planet would appear. This planet was Neptune, and it was found in 1846, proving that Newson's law was correct.

It was Neptune's gravitational pull that was affecting the orbit of Uranus.

Gravity, The Moon, And Tides

We've found that gravity is the force of attraction between two objects.

Every particle of matter is attracted to every other particle in the galaxy, but the force exerted between individual particles is very small, because their mass is very small.

But with large objects, such as the moon and the Earth, the force of attraction is very strong.

So strong, in fact, that it's enough to keep the moon spinning around the Earth, rather than flying off into space.

(The mass of the Earth is around 6 million million million million kg.)

Because the moon is smaller, and less dense, than Earth, it has a significantly smaller mass. Therefore the force of gravity on the moon is much smaller. Around 17% of the Earth's, in fact.

Neil Armstrong's weight on the moon was only 17% of what it was on Earth. This enabled him to jump higher than he could on Earth, but was still enough to bring him back to the Moon's surface.

Although the mass of the moon is much less than that of Earth's, it still affects the Earth. The force it exerts as it orbits the Earth pulls the oceans towards it, causing tides.

Gravity For Kids Conclusion

We've covered a lot in this article. Thanks to Galileo you've found that all objects (a stone, you, a grand piano) fall at the same rate, no matter what their mass.

Again, thanks to Galileo, you've found that on Earth, objects accelerate at 9.81 m/s² (give or take) when dropped, and that this figure varies ever so slightly depending on where you are on the Earth.

Newton's work showed us that gravity is a force of attraction between objects, and is dependent both on the masses of the objects involved, and on the distance they are from each other.

From this you know that the force of attraction increases for an object with more mass, and decreases for an object with less mass, meaning that their acceleration is a constant, G.

We've found that the moon is responsible for pulling the seas towards it, making the tides go out and come back in again.

Why not read more about the lives and work of the scientists in the article? Many of them made other incredible discoveries that were not just related to gravity.

See more science articles here.

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