Mechanics · Physics

Toppling or Sliding Simulation

Q: Why does the normal force move when a block is pushed?

The push tries to turn the block about its front edge. The normal force moves forward to provide an opposite torque; when it reaches the edge it can move no further, and the block tips.

Q: When does a block on an incline tip over?

When the vertical line through its centre of mass falls outside its base, that is when tan θ > b/h.

Push a block or tilt the floor beneath it and find out whether it slides or tips over first. See the normal force shift towards the edge as the push grows.

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

Chapter: Laws of Motion · System of Particles
For: Class 11 · JEE
Time: ~10 min

Toppling or Sliding is a Pro simulation

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How to use it

1Choose Push a block or Tilt the floor.
2Set the block's base, height, mass and the friction.
3Raise the force (or the angle) and see which happens first.
4Show forces to see friction, weight and the normal force.

What to notice

Pushed at height y, a block tips before sliding if y > b/2μ.
At rest the normal force moves forward by F·y/mg to balance the torque.
On an incline it slides when tan θ > μ and tips when tan θ > b/h.
Tall, narrow blocks tip; squat ones slide.

For teachers

A ready-made teaching kit comes with this lab

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

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About the Toppling or Sliding simulation

Push a box near its base and it slides; push it near the top and it tips over. Which happens first depends on two thresholds. Sliding starts when the push beats limiting friction, μmg. Tipping starts when the push's turning effect about the front edge beats that of the weight, F·y > mg·b/2. Before either, the normal force shifts forward to keep the box from turning.

This toppling simulation lets you push a block at any height on a rough floor, or tilt the floor under it. It shows friction, weight and the shifting normal force, tells you which threshold is lower, and animates the slide or the topple. It is a standard Class 11 and JEE problem on friction and rotational equilibrium.

Also covers: toppling condition, block on incline topple, slide or topple, normal force shift, friction torque.

Frequently asked questions

What is the condition for a block to topple before it slides?

When pushed at height y, it topples first if y > b/(2μ), where b is the width of its base. On an incline it topples first if b/h < μ.

Why does the normal force move when a block is pushed?

The push tries to turn the block about its front edge. The normal force moves forward to provide an opposite torque; when it reaches the edge it can move no further, and the block tips.