54869782-Physics-Revision-Guide-PDF

# 54869782-Physics-Revision-Guide-PDF - PHYSICS REVISION...

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PHYSICS REVISION GUIDE Ch1: Physical Measurement SI units: metre, kg, second, ampere, Kelvin, mole, candela. Derived: volume, density. 1.2 Measurement Uncertainty = 0.5x the smallest value. Random error: lots of slightly different readings. Experimental error: problem with measuring device/method. Percentage uncertainty = uncertainty/value Adding values = add uncertainties. Ch2: Mechanics 2.1 Kinematics Velocity = displacement per unit time. Speed = distance travelled per unit time. Relative velocity = subtract the vectors. Acceleration = ∆velocity/time Average velocity = displacement/time SUVATS: a = (v - u)/t s = (u + v)t/2 s = ut + 0.5at 2 v 2 = u 2 + 2as Positive displacement/velocity = body moving right. 2.2 Free-Fall Motion On Earth, bodies fall with an acceleration of 9.81ms -2 . When falling, air resistance will push you up more and more until you cannot go faster. Area beneath a velocity-time graph = displacement.

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2.4 Projectile Motion SUVAT for horizontal motion: R = v cos Θ t SUVAT for vertical motion: h = v 2 sin 2 Θ/2g and t = 2vsinΘ/g 2.5 Forces and Dynamics Gravitational force: W = mg. (W = weight). Free body diagrams show the forces acting on objects. 2.6 Newton’s First Law of Motion First law: “A body will remain at rest of moving with constant velocity unless acted upon by an unbalanced force.” Examples: mass on a string (T = mg), parachutists (force up = force down), car (force left = force right). Translational equilibrium: all forces are balanced. 2.7 Force and Acceleration Momentum, ρ = mv. Impulse: movement due to the effect of something. Impulse is the change in momentum. Newton’s second law of motion: “the rate of change of momentum of a body is directly proportional to the unbalanced force acting on that body, and takes place in the same direction.” So, F = ma. 2.8 Newton’s Third Law Newton’s third law of motion: “if body A exerts a force on body B then body B will exert an equal and opposite force.”
Example: a box on the floor, water hitting a wall. Law of conservation of momentum: “in a system of isolated bodies, the total momentum is always the same.” Area under a force-time graph = impulse. 2.9 Work, Energy, Power Work done = force x distance moved in direction of force. In general: Work = FcosΘ x ∆s (Θ is the angle between s and F). Work done by a varying force: use average force, or find the area under a force-distance graph. F/∆s = K (spring constant). Gravitational potential energy (PE): the energy a body has due to its position above the Earth. PE = mgh. Law of conservation of energy: “energy can be neither created or destroyed - only changed from one form to the other.” Elastic collision: when both momentum and KE are conversed. Inelastic collision - momentum/KE not conserved. For example when two bodies stick

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54869782-Physics-Revision-Guide-PDF - PHYSICS REVISION...

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