Forces, mass and weight

Learning objectives

Distinguish mass (the quantity of matter in an object) from weight (the gravitational force on it), and use W = mg with g as the gravitational field strength in N/kg

Describe how forces can change the size, shape, speed or direction of motion of an object, and find the resultant of two or more forces acting along the same straight line

Know that an object stays at rest or keeps a constant velocity unless a resultant force acts on it, and at Extended use F = ma with the acceleration in the direction of the resultant force

Describe solid friction, and drag in liquids and gases (including air resistance), as forces that oppose motion and produce heating

Plot and interpret load–extension graphs for a spring or elastic solid and describe the experiment, and at Extended define the spring constant k = F/x and identify the limit of proportionality

Explain qualitatively how a force perpendicular to the motion keeps an object moving in a circle, and how the force needed depends on the speed, the radius and the mass (Extended)