Stability

Question 1

Define the term stable equilibrium

Answer 1

A body that is displaced then released but returns to its equilibrium position

Question 2

Why does an object in stable equilibrium return to equilibrium when displaced and released?

Answer 2

The centre of mass of the object is directly below the point of support when object is τ rest. Therefore the support force are directly equal and opposite to each other when object is in equilibrium. However, at the instant release, the line of action of the weight no longer passes through the point of support, so the weight returns to equilibrium

Question 3

Define an unstable equilibrium.

Answer 3

A body where after displacement and release will not return to equilibrium

Question 4

Why do bodies in an unstable equilibrium not return to equilibrium after displacement and release?

Answer 4

The centre of mass is directly above the point of support when it’s in equilibrium. Support forces are equal and opposite to the weight. If body is displaced slightly, the centre of mass would no longer be above the point of support, therefore weight acts to turn the plank further from equilibrium

Question 5

Explain tilting.

Answer 5

Where an object at rest on a surface is acted on by a force that raises it up on one side

Question 6

Explain the act of toppling

Answer 6

A tilted object will topple over if its tilted too far. The line of action of its weight passes closer and closer to its pivot and then beyond

Question 7

Explain objects on a slope

Answer 7

A tall object on a slope will topple over if the slope is too great. This will happen if the line of action of the weight lies outside the wheelbase of the vehicle.

Question 8

Explain the forces acting on a vehicle on a slope

Answer 8

The sideways friction, F, the support forces Sx and Sy, and the force of gravity on the vehicle act.
Resolving these forces parallel and perpendicular to the slope gives:
1. Parallel to the slope:
F= WsinX
2. Perpendicular t the slope:
Sx+ Sy= WcosX