H2 Physics - Forces & Moments

State the 4 fundamental forces in nature

• Gravitational force

• Electromagnetic force

• Strong nuclear force

• Weak nuclear force

Define the center of gravity

The center of gravity of a body is the point at which the weight of the body, or the resultant of the distributed gravitational attraction on the body, appears to act.

State what the viscous force is

It is the force that arises when an object moves through a fluid, which it then imparts momentum to the fluid molecules, hence causing itself to slow down.

Define Hooke’s Law.

The extension of a body is proportional to the applied load if the limit of proportionality is not exceeded.

Define a moment of a force.

The moment of a force about an axis is the product of the force and the perpendicular distance of the line of action of the force from the axis.

Define a couple.

A couple is something which consists of a pair of equal and opposite forces whose lines of action do not coincide.

State the conditions for a body to be in equilibrium.

• The body needs to be in both translational and rotational equilibrium.

• The resultant force on the body is zero.

• The resultant moment on the body about any axis is zero.

Define the torque of a couple.

It is the product of the magnitude of one of the forces and the perpendicular distance between the forces.

State the conditions for 3 coplanar forces acting on a body in equilibrium

The line of action are either parallel or all meet at a point.

State the Principle of Moments

For a body in equilibrium, the sum of all clockwise moments about any axis must equal the sum of all anticlockwise moments about the same axis.