Key Physics Concepts and Forces
Hooke's Law is surprisingly simple - when you stretch a spring, the extension is directly proportional to the force you apply (as long as you don't overstretch it). The formula F = kx shows this relationship, where k is the spring constant that tells you how stiff the spring is.
Understanding the difference between mass and weight is crucial for exams. Mass is a scalar quantity (just a number with size only) measured in kg, whilst weight is a vector (has both size and direction) measured in Newtons. Your mass stays the same everywhere, but your weight changes - you'd weigh less on the Moon because gravity is weaker there!
The principle of moments explains why seesaws balance. When something's in equilibrium, the clockwise moments equal the anticlockwise moments about the pivot. A moment is simply the turning effect of a force, calculated as Force × perpendicular distance from the pivot.
Quick Check: Remember that weight = mass × gravitational field strength , where g = 10 N/kg on Earth.
Energy and Radioactivity Fundamentals
Energy conservation is one of physics' most important principles - energy can change from one form to another, but the total amount never changes. This applies everywhere from roller coasters (potential energy converting to kinetic) to power stations.
Efficiency measures how good a device is at transferring energy usefully. It's calculated as useful output ÷ total input, and it's always less than 1 (or 100%) because some energy is always wasted, usually as heat.
Radioactivity occurs when unstable nuclei decay to become stable, releasing radiation like alpha particles (2 protons + 2 neutrons), beta particles (fast electrons), or gamma rays (high-energy electromagnetic waves). Half-life is the time it takes for half the radioactive nuclei to decay - this varies enormously between different isotopes.
Understanding atomic structure helps explain radioactivity. The atomic number tells you the number of protons, whilst the mass number is protons plus neutrons. Isotopes are atoms of the same element with different numbers of neutrons.
