Mechanics · Physics

Pseudo Force in Accelerating Frames Simulation

Watch a pendulum in a truck, a block on a cart's wall and a ball on a bus floor, from the road and from inside. Inside an accelerating vehicle, adding the pseudo force −ma₀ makes Newton's laws work again.

Interactive virtual lab · no download · works on phones and laptops

Chapter: Laws of Motion (NLM)
For: Class 11 · JEE
Time: ~12 min

Pseudo Force in Accelerating Frames is a Pro simulation

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How to use it

1Pick a situation from the tabs.
2Switch between the view from the road and from inside.
3Change the acceleration and press play.

What to notice

From the road only real forces act, and ΣF = ma.
Inside a frame accelerating at a₀, add −ma₀ to every body; then ΣF = 0 for anything at rest there.
A pendulum in the truck settles at tan θ = a₀/g.
A block stays on the cart's front only if a₀ ≥ g/μ.

For teachers

A ready-made teaching kit comes with this lab

Lesson plan
19 min, 4 steps
Ask the class
3 questions with answers
Quick quiz
5 questions, printable
Key formulas
3 formulas

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About the Pseudo Force in Accelerating Frames simulation

Newton's laws hold in inertial frames, ones that are not accelerating. Inside an accelerating vehicle they appear to fail: a pendulum leans back with no visible push, a ball rolls to the back of a bus on its own. To use F = ma in such a frame we add a pseudo (fictitious) force −ma₀ on every body, opposite to the frame's acceleration a₀.

This pseudo force simulation shows three classic cases — a pendulum hanging in a truck, a block held on the front of an accelerating cart, and a ball on a smooth bus floor — and lets you switch between the view from the road and the view from inside. From the road only real forces act and they give ma₀; from inside the body is at rest, and the real forces plus the pseudo force add to zero. Both views give the same answers.

Also covers: pseudo force, fictitious force, non inertial frame, inertial frame, pendulum in accelerating car, block on accelerating cart wall, accelerating bus, frame of reference.

Frequently asked questions

What is a pseudo force?

A force we add when describing motion from an accelerating frame: −m times the frame's acceleration. No object exerts it, so it has no reaction pair.

Why does a pendulum lean backwards in an accelerating car?

From the road, the string must pull forwards as well as up to accelerate the bob with the car, so it tilts back until tan θ = a/g.

When do you need a pseudo force?

Only when you choose to solve a problem in an accelerating frame. Solving the same problem from an inertial frame needs no pseudo force and gives the same result.