Forces

Notes

What you need to know

• State the effects a force can have on an object: change shape, speed or direction
• Distinguish between contact forces (friction, normal reaction, tension) and non-contact forces (gravity, magnetic, electrostatic)
• Calculate the resultant of forces acting along the same straight line
• Draw and interpret free body diagrams with labelled force arrows
• State Newton's First Law: an object remains at rest or moves at constant velocity unless a resultant force acts on it
• Recall and use F = ma to calculate resultant force, mass or acceleration
• State Newton's Third Law and identify Newton's Third Law pairs
• State that extension is directly proportional to force, within the limit of proportionality (Hooke's Law)
• Recall and use F = ke, where k is the spring constant
• Describe and interpret a force–extension graph including the limit of proportionality and elastic limit
• Define the moment of a force as M = F × d and use the principle of moments for equilibrium
• Define centre of gravity and describe how to find it for a flat lamina by suspension
• Explain the conditions that affect stability in terms of centre of gravity and base area

Syllabus subtopics

• Effects of forces and deformation
• Hooke's Law and spring constant
• Resultant forces
• Newton's Laws of motion
• Friction and drag
• Moments and turning effects
• Principle of moments
• Centre of gravity and equilibrium