KnowSoda
SciencePhysics
Motion & Forces: fun facts and quiz
The essentials in 7 ideas, with fun facts, an illustrated story and a quiz to see how much you know.
The essentials
Inertia
Things keep doing what they’re doing unless a force changes it. A ball at rest stays put; a sliding puck keeps sliding until friction slows it.
Key fact
This is Newton’s first law of motion.
Force & Acceleration
Push something harder and it speeds up faster; make it heavier and it speeds up more slowly. Force equals mass times acceleration.
Key fact
Newton’s second law: F = m × a.
Action & Reaction
Forces come in pairs. When you push on a wall, it pushes back on you; a rocket pushes gas down, and the gas pushes the rocket up.
Key fact
Newton’s third law: every action has an equal and opposite reaction.
Gravity
Gravity pulls every mass towards every other mass. Near Earth’s surface, it speeds falling things up by about 9.8 metres per second, every second.
Key fact
Without air, a feather and a hammer fall at the same rate.
Friction
Friction resists things sliding past each other. It lets tyres grip the road and shoes grip the floor, and it turns motion into heat.
Key fact
Rub your hands together: the warmth you feel is friction.
Speed & Velocity
Speed is how fast something moves. Velocity is speed with a direction. A car taking a bend at a steady 50 km/h has a changing velocity.
Key fact
Changing direction counts as accelerating, even at a steady speed.
Momentum
Momentum is mass times velocity. A slow lorry can have more momentum than a fast bike, which is why heavy things are so hard to stop.
Key fact
In a collision, the total momentum stays the same.
Fun facts
Seatbelts exist because of inertia: in a sudden stop, your body keeps moving forward.
The newton is named after Isaac Newton, who set out the laws of motion.
Squid and octopuses jet through the sea by squirting water backwards: the water pushes them forwards.
On the Moon in 1971, Apollo 15 astronaut David Scott dropped a hammer and a feather. They landed at the same time.
Geckos climb walls without glue: millions of tiny hairs on their toes cling by sheer closeness to the surface.
Usain Bolt hit about 44 km/h during his 2009 world-record 100 metres.
Newton’s cradle shows momentum passing along a row of balls: swing one in, and one swings out the far side.
Story: The Apple and the Moon
The Apple and the Moon
1666. Plague shuts Cambridge University, and young Isaac Newton goes home to his family’s farm.
There, he later said, a falling apple set him wondering: could the pull that brings it down reach all the way to the Moon?
It could. His law of gravity, published in 1687, explained falling apples and orbiting planets with one idea.
True or false?
Tap your answer to see if you got it, and why.
-
Question 1 of 10
A moving object with no force on it keeps moving at the same speed.
Show the answer
True. With nothing to slow it down, it would carry on forever.
-
Question 2 of 10
The same push speeds up a light cart more than a heavy one.
Show the answer
True. Less mass means more acceleration for the same force.
-
Question 3 of 10
Rockets need air to push against in order to fly.
Show the answer
False. They push exhaust out the back, and the exhaust pushes them forward, even in space.
-
Question 4 of 10
Heavier objects always fall faster than lighter ones.
Show the answer
False. Without air resistance they fall together. Air just slows light, spread-out things.
-
Question 5 of 10
Friction always acts against sliding motion.
Show the answer
True. It pushes the opposite way to the slide.
-
Question 6 of 10
Velocity includes a direction; speed does not.
Show the answer
True. 50 km/h is a speed. 50 km/h north is a velocity.
-
Question 7 of 10
A heavy lorry moving slowly can have more momentum than a fast bicycle.
Show the answer
True. Its huge mass makes up for its low speed.
-
Question 8 of 10
An object needs a constant push to keep moving at a steady speed.
Show the answer
False. The push only makes up for friction. Without friction, it would glide on.
-
Question 9 of 10
Doubling the force on an object halves its acceleration.
Show the answer
False. Doubling the force doubles the acceleration.
-
Question 10 of 10
When you jump, you push the Earth down a tiny bit.
Show the answer
True. The Earth is so massive that the effect is far too small to notice.
Keep going in the app
KnowSoda learns what you know and brings back what you’re about to forget. Motion & Forces has 6 more ideas at the Advanced and Expert levels.
