Forces and resultant forces

The idea

Scalars have magnitude only (speed, distance, mass, time); vectors have magnitude and direction (velocity, displacement, force, acceleration). Forces are contact (friction, air resistance, tension, normal contact) or non-contact (gravity, magnetic, electrostatic). Weight W = mg, measured with a newtonmeter. The resultant force is the single force with the same effect as all the forces acting together.

1. Classify the quantity.
2. For forces along a line, add those in one direction and subtract the others.
3. Use W = mg with g = 9.8 N/kg.

Watch out Mass (kg) and weight (N) are different: weight depends on the gravitational field strength.