Gravity, friction and simple machines
I can explain why things fall, name the forces that slow things down, and say how levers, pulleys and gears help.
For grown-ups: this lesson in words
Years 5 and 6 · Science
Gravity, friction and simple machines: I can explain why things fall, name the forces that slow things down, and say how levers, pulleys and gears help.
Here is a ball falling towards the ground. Nothing is holding it up, so we say it is unsupported.
The long arrow pointing down is gravity. Gravity is a pull between the Earth and the ball.
The short arrow pointing up is air resistance. Gravity is much bigger, so the ball speeds up as it falls.
Gravity pulls things towards the Earth. That is why things fall when nothing holds them up.
Picture: A drawing of forces acting on something moving. A ball falls. Gravity pulls it down and air resistance pushes up a little: the gravity arrow is much longer, so the ball speeds up. Labels: object, gravity and air resistance.
Here is a person coming down under a parachute.
Gravity pulls the person and the parachute down towards the Earth.
Air resistance pushes up. The big cloth canopy pushes against lots of air, so air resistance is big.
The two arrows are the same length, so the parachute falls slowly and steadily. It has not stopped.
Picture: A drawing of forces acting on something moving. A parachute falls. Gravity pulls it down and air resistance pushes up on the big canopy: the arrows are the same length, so it falls at a slow, steady speed. Labels: object, gravity and air resistance.
Your turn: This ball is falling. One arrow has a ? instead of a name. Which force does the arrow marked ? show?
Picture: A drawing of something moving, with arrows. A ball is dropping towards the ground. A long arrow points straight down and a short arrow points straight up. A label marked ? points to the arrow pointing straight down, towards the ground.
Choose one:
- Gravity
- Air resistance
- Friction
Answer
The answer: Gravity
Gravity. It pulls the ball down towards the Earth.
Picture: A drawing of forces acting on something moving. A ball falls. Gravity pulls it down and air resistance pushes up a little: the gravity arrow is much longer, so the ball speeds up. Labels: object, gravity and air resistance.