FORCES AND MOMENTUM - Chapter 1

Forces and Newton’s 1st Law

What is a force?

A force is a push or pull that acts on an object due to interaction with another object.

What is the SI unit of force?

Newton (N)

What is a resultant force?

Sum of all forces acting on an object

when do we subtract forces

We subtract forces when they are acting in opposite directions.

List 4 non-contact forces.

• Gravitational force

• Magnetic force

• Electrostatic force

• Weight

List 5 contact forces.

• Friction

• Air resistance (drag)

• Tension

• Normal contact force

• Upthrust

What is the SI unit of weight?

Newton (N) (same as force, because weight is a force)

What is the equation for weight?

1. Weight = Mass × Gravitational field strength
   W=m×g

What is Newton’s First Law?

An object’s velocity only changes when there is a resultant force

What do resultant forces cause?

Resultant forces cause a change in the motion of an object

Can an object with 0N resultant force be moving?

Yes, an object with 0 N resultant force can be moving at a constant velocity

Describe the motion of a rocket with a resultant force of 10,000 N upwards.

The rocket will accelerate upwards because the large resultant force causes an upward acceleration.

Describe the motion of a car with a thrust of 500 N and 500 N of friction on it.

The car will move at a constant speed because the thrust and friction forces balance each other, resulting in zero resultant force.

When do objects slow down?

Objects slow down when there is a resultant force acting opposite to their direction of motion, such as friction or air resistance.