Rocket runs across the lawn with his hand flat and open, palm forward. "I can feel the air pushing!"
He runs back with his hand turned sideways, thumb forward. "Now it barely pushes at all."
Raven writes both results in the Field Log. "What do you notice? Same hand, same run, different push."
Nova glides beside them. "What changed about the hand?" she asks. "Not its weight."
"The part facing the air," Rocket says. "Flat hand, big face. Sideways hand, small face."
Raven holds up the flat paper and the crumpled ball from yesterday. "Same paper, different face."
"So the air pushes harder on a big face," Rocket says. Nova dips in a little nod. "Scientists call that push drag."
Drag is the force on an object when it moves through a fluid, which means a gas or a liquid. Air is a gas, so moving through air makes drag.
You feel drag when you move your hand through water. You can feel it when you move your hand in a strong wind.
The faster you move your hand, the harder it is to move. Like friction, drag always opposes the motion of the object.
Tilt your hand so only the edge goes forward, and the drag gets smaller. You decreased the area facing the direction of motion.
The size of the drag depends on the shape of the object, its size, its speed and the fluid it moves through.
A NASA guide puts it simply. If there is no fluid, there is no drag. If there is no motion, there is no drag.
A falling object in the air has two forces on it. Gravity pulls it down, and drag pushes up against the fall.
Think of a skydiver. The downward pull of gravity stays the same no matter how fast the skydiver falls.
Drag is different. As the skydiver speeds up, the drag grows. It keeps growing until it equals the pull of gravity.
Then the two forces are balanced. The forces add up to zero, so the speed stops changing. The skydiver falls at a steady speed.
That steady speed is called terminal velocity. A heavier skydiver must fall faster before the drag grows enough to balance the weight.
The flat paper reaches a slow terminal velocity almost at once. The crumpled ball has a smaller face, so it must fall faster to do the same.
| Statement | True or false? |
|---|---|
| Drag gets bigger as an object moves faster. | ? |
| The pull of gravity on a skydiver gets bigger as the skydiver speeds up. | ? |
| A heavier skydiver reaches a faster terminal velocity than a lighter one of the same shape. | ? |
| An object falling in a vacuum feels drag. | ? |
Good thinking. Tomorrow is Field Lab: you will measure how far a ball rolls on three surfaces and race two sheets of paper.