Side A3: Forces, Density, Pressure and Dynamics

understand that mass is the property of an object that resists change in motion

recall F = ma and solve problems using it, understanding that acceleration and resultant force are always in the same direction

define and use linear momentum as the product of mass and velocity

define and use force as rate of change of momentum

state and apply each of Newton’s laws of motion

describe and use the concept of weight as the effect of a gravitational field on a mass and recall that the weight of an object is equal to the product of its mass and the acceleration of free fall

show a qualitative understanding of frictional forces and viscous/drag forces including air resistance (no treatment of the coefficients of friction and viscosity is required, and a simple model of drag force increasing as speed increases is sufficient)

describe and explain qualitatively the motion of objects in a uniform gravitational field with air resistance

understand that objects moving against a resistive force may reach a terminal (constant) velocity

state the principle of conservation of momentum

apply the principle of conservation of momentum to solve simple problems, including elastic and inelastic interactions between objects in both one and two dimensions (knowledge of the concept of coefficient of restitution is not required)

recall that, for an elastic collision, total kinetic energy is conserved and the relative speed of approach is equal to the relative speed of separation

understand that, while momentum of a system is always conserved in interactions between objects, some change in kinetic energy may take place

understand that the weight of an object may be taken as acting at a single point known as its centre of gravity

define and apply the moment of a force

understand that a couple is a pair of forces that acts to produce rotation only

define and apply the torque of a couple

state and apply the principle of moments

understand that, when there is no resultant force and no resultant torque, a system is in equilibrium

use a vector triangle to represent coplanar forces in equilibrium

define and use density

define and use pressure

derive, from the definitions of pressure and density, the equation for hydrostatic pressure ∆p = ρg∆ h

use the equation ∆p = ρg∆ h

understand that the upthrust acting on an object in a fluid is due to a difference in hydrostatic pressure

calculate the upthrust acting on an object in a fluid using the equation F = ρgV (Archimedes’ principle)