A car takes a sharp left turn, and you slide across the seat toward the right door. It feels exactly like being flung outward, as if some force grabbed you and threw you at the door.
You have just seen that no outward force acts on a circling object. So what is really happening?
Run the moment in slow motion, seen from above. Before the turn, you and the car move straight ahead together, at the same velocity.
The turn begins. The road's friction acts on the car's tires and turns the car's path to the left.
That friction acts on the car, not on you. Sitting on a slick seat, you have almost no force acting on you in the horizontal plane.
From above, the picture is plain. Your path stays straight while the car's path bends left, out from under you. The right door swings toward you.
Inside the car, you only feel the result: the door seems to rush at you, and your body seems flung toward it. The feeling is real. The outward force is not. Nothing threw you outward: the car turned, and you did not.
Then the door reaches you. The door exerts a normal force on you, toward the center of the turn, and that normal force supplies your centripetal force. You turn with the car for the rest of the curve.
A city train curves left, and a standing passenger holding nothing drifts toward the right wall. Why?
A bus turns right, and a standing rider holding nothing drifts toward the bus's left wall. Explain why, naming any forces that act.
The road's friction turns the bus to the right; it acts on the bus's tires, not on the rider.
Almost no horizontal force acts on the rider, so the rider's body keeps its straight-line velocity.
The bus's path bends right while the rider's path stays straight, so the left wall moves toward the rider.
No force moved the rider toward the wall. The bus turned right under the rider, whose body continued straight, and the left wall came to meet him.
As the family car turns sharply left, Nestor slides across the slick seat to the right door. He says: 'Something pushed me toward the door.' Is he correct?
A note on the cases in this lesson: each vehicle turns at a steady speed on level ground, and drag is small enough to ignore. The horizontal forces that matter are the ones named.
A gym bag rests on the slick back seat as a car turns right. The bag ends against the left door. Did a force act on the bag toward that door?
The slick seat gives the bag almost no friction, so almost no horizontal force acts on the bag.
The bag keeps its straight-line velocity while the car's path bends right.
Relative to the turning car, the bag moves toward the left door, with no leftward force acting on it.
No. The bag kept moving straight while the car turned right beneath it; the door moved to the bag.
Odile stands on a curving airport shuttle. She says: 'During the turn, no force on me points toward the outside of the curve.' Is she correct?
A school van rounds a left bend. A duffel bag rests on the van's slick rear floor. Against which side of the van does the bag end up?
As a pickup turns left, a toolbox on its slick flat bed slides toward the right side of the bed. Which statement explains the slide?
A passenger slides across the slick back seat of a car turning right, until she reaches the left door. For the rest of the turn she moves in a circle with the car. Which force supplies her centripetal force from then on?