Unit 4
Forces.
What changes how a body moves: Newton's three laws, weight and the normal force, friction, and force diagrams.
Before this unit
The unit, lesson by lesson
Lessons
5 lessons · 23 practice questions · about 2 hours
The first law: force and motion
Does a body need a force to keep moving? A fan cart on a track with no friction, what happens when the fan switches off, and forces that balance each other.
The second law: force, mass and acceleration
How much acceleration a force gives: the link between force, mass and acceleration, the newton as a unit, and what happens when several forces act on the same cart.
The third law, weight and the normal force
Forces come in pairs: the fan and the air, the Earth and the cart. Weight, the normal force, and why an action–reaction pair does not cancel itself.
A free-body diagram on a slope
A wooden block resting on a slope: how to draw every force acting on it, split its weight into two components, and find the normal force and the friction.
Static and kinetic friction
How much friction can hold, at what angle a block starts to slide, and how fast it then speeds up.