A force is something that acts upon an object, often to make it move or to slow it down from moving, such as air resistance, although sometimes it is just there without us realising it like gravity, which stops us from floating into the sky. Forces are measured in a unit called 'Newtons' after Isaac Newton.
Different forces affect us literally every second of every and without them we wouldn’t be able to exist. The main forces that we cover in our primary rockets workshops are thrust, friction, air resistance, and gravity and we also cover lift in our aeroplane task in our incredible inventions workshop, which is a force that, as the name suggests, lifts aeroplanes from the ground.
(Teachers, this is covered in much more detail in our science workshops)
Gravity is what is holding you to the floor right now. It’s the force that pulls objects together, though you’ll only really notice it with very large objects like the Earth or The Sun. To really understand how important gravity is, we’ll have to work backwards and consider life without it. Firstly, if there was no gravity, nothing that isn’t stuck to the earth would stay on it! We also wouldn’t be here in the first place because it is gravity that keeps us in our orbit around The Sun and squished together all the molecules into the Earth in order to make it!
So you see, without gravity, we’d be nothing more than particles created by the big bang, floating endlessly through space, never meeting or touching, which would be a very lonely existence indeed.
Air resistance (also called drag) is the reason why a flat piece of paper falls to the floor much more slowly than a scrunched up piece. Try it with two pieces of paper the same size and you will see what I mean.
The reason is because when an object moves through the air, the particles of air that it hits pushes back against it like a crowd of people trying to stop it moving and the more particles it comes into contact with, the greater the push.
A flat piece of paper therefore has a bigger surface than a scrunched up piece, because nothing is folded over. This means that there are many more of those tiny particles of air which creates more push against the opened paper compared to the scrunched paper.
The effects of air resistance can be seen everywhere - it’s essential for allowing birds and planes to fly, it changes the way we design things like cars and even bridges, and let’s just say that skydiving would be much less popular without it!
Thrust is a force called a ‘reaction force’ which moves an object forward, normally an aeroplane or a rocket, but also a car (such as our rocket car activity in our Incredible Inventions workshop) or even a boat.
It is best witnessed in a rocket launch such as the launches of model rockets in our Rockets to Rovers workshop, when the rocket is forced upwards by the downwards thrust of the rocket engines. The amount of thrust required to lift a rocket is a very important calculation to make if you are a rocket scientist, because unlike a car that will just stop with too little thrust, a rocket will fall to earth!
Friction is the force that is created when two surfaces are rubbed together. Different surfaces and materials generate different amounts - try rubbing the back of your hand on a surface, and then the front of your fingers. Which was harder to move? Unless you’re wearing gloves (in which case, take them off and try again, silly) then your fingers should have been harder to move because of your fingerprints.
Often, the rougher an object is, the more friction it generates. For example, car tyres are made out of rubber so they generate lots of friction and grip to the tiny bumps on the road, just like our scale moon rover, which sticks to our pretend moon surface perfectly! If the tyres were made of shiny metal that didn’t mould to the shape of the bumps, they’d be skidding everywhere! Not to mention that nobody would be able to travel in summer!
Lift is quite a complex force based on something called ‘Bernoulli’s principle’, and is be explained more in our article how planes fly.
Put simply, lift is what makes a plane go up. As the wings move through the air, the air above the wing moves faster, whilst the air below it moves slower. The slower air underneath builds up a much higher air pressure, which means more particles of air are in one place. Because there are more underneath, they push the wings up, pushing the rest of the plane up. When the amount of lift generated is more than the weight of the plane, it takes off.
This is how birds, planes and even paper airplanes fly, or at least glide. With style. This is explored in much greater detail when we look at the invention of the aeroplane in our Incredible Inventions primary workshop with scale models and a fun paper plane task.
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