Hold your hand out a car window at highway speed, palm forward. The air shoves it backward, hard. At parking-lot speed, the same hand barely feels a thing.
Air can push, and how hard it pushes depends on how fast you move through it.
The hand out the window moves forward through the air, and the air pushes it backward. A cyclist coasting fast feels the same: the air pushes back against her motion.
A skydiver falls downward through the air, so the air pushes upward on him.
The pattern so far: the push is always opposite to the object's motion through the air.
A cyclist coasts westward on a calm day. The air's drag on her points:
And it grows with speed: at highway speed the hand is shoved hard, at parking-lot speed barely at all. The faster the object moves, the stronger the push.
A pitcher throws a slow warm-up pitch, then a fast one with the same ball. Which pitch feels the larger drag from the air?
Water does the same to a swimmer gliding through it. Air and water are both fluids: stuff that flows.
So: a fluid pushes back on an object moving through it, opposite to the object's motion, and more strongly the faster the object moves. This friction-like force is called drag. When the fluid is air, it is also called air resistance.
A maple seed spins straight down toward the ground. The air's drag on it points:
You have already met air resistance by name: free fall meant falling with air resistance ignored. Drag is that ignored influence, now defined as a force.
A swimmer glides westward underwater after pushing off the pool wall. Which direction is the drag on her, and what exerts it?
A fluid pushes back on an object moving through it, opposite to its motion.
The fluid here is the water, and she moves westward through it.
The water exerts the drag, pointing eastward: opposite her motion.
A skydiver's downward speed keeps climbing after he jumps. What happens to the drag on him as he speeds up?
Drag grows stronger as the object moves faster through the fluid.
The drag grows stronger, still pointing upward, opposite his downward motion.
A parachutist descends straight down at a steady clip. Which statement names the drag force on her?
A kayak glides north across a still lake. The water's drag on the kayak points:
A race car accelerates down a straightaway. As its speed climbs, the drag on it: