Forces and Newton's Laws
Scalar quantities (like speed) only have size, whilst vector quantities (like velocity) have both size and direction - think of it like the difference between saying "30 mph" versus "30 mph north". Forces are vectors, which is why we draw them as arrows where the length shows the strength.
Forces split into two types: contact forces (like friction and air resistance) need objects to touch, whilst non-contact forces (like weight and magnetism) work at a distance. Newton's three laws govern how forces work: objects keep doing what they're doing unless a resultant force acts on them, force equals mass times acceleration, and every action has an equal and opposite reaction.
Mass (measured in kg) tells you how much matter something contains and stays constant everywhere, but weight (measured in N) is the gravitational force acting on that mass and changes depending on gravity's strength. When multiple forces act on an object, you find the resultant force by adding them as vectors - sometimes using scale diagrams or Pythagoras' theorem.
💡 Quick Check: If you're in a lift accelerating upwards, you feel heavier because there's a resultant force - your weight plus the extra force needed for acceleration!
