Forces, Moments & Vectors

Know that the following quantities are scalars: distance, speed, time, mass, energy and temperature

Know that the following quantities are vectors: force, weight, velocity, acceleration, momentum, electric field strength and gravitational field strength

Determine, by calculation or graphically, the resultant of two vectors at right angles, limited to forces or velocities only

State that the acceleration of free fall g for an object near to the surface of the Earth is approximately constant and is approximately 9.8 m / s2

Describe the motion of objects falling in a uniform gravitational field with and without air/liquid resistance, including reference to terminal velocity

State that mass is a measure of the quantity of matter in an object at rest relative to the observer

State that weight is a gravitational force on an object that has mass

Define gravitational field strength as force per unit mass; recall and use the equation W g = m and know that this is equivalent to the acceleration of free fall

Know that weights (and masses) may be compared using a balance

Describe, and use the concept of, weight as the effect of a gravitational field on a mass

Define density as mass per unit volume; recall and use the equation m ρ = V

Describe how to determine the density of a liquid, of a regularly shaped solid and of an irregularly shaped solid which sinks in a liquid (volume by displacement), including appropriate calculations

Determine whether an object floats based on density data

Determine whether one liquid will float on another liquid based on density data given that the liquids do not mix

Know that forces may produce changes in the size and shape of an object

Sketch, plot and interpret load–extension graphs for an elastic solid and describe the associated experimental procedures

Determine the resultant of two or more forces acting along the same straight line

Know that an object either remains at rest or continues in a straight line at constant speed unless acted on by a resultant force

State that a resultant force may change the velocity of an object by changing its direction of motion or its speed

Describe solid friction as the force between two surfaces that may impede motion and produce heating

Know that friction (drag) acts on an object moving through a liquid

Know that friction (drag) acts on an object moving through a gas (e.g. air resistance)

Define the spring constant as force per unit extension; recall and use the equation F k = x

Define and use the term ‘limit of proportionality’ for a load–extension graph and identify this point on the graph (an understanding of the elastic limit is not required)

Recall and use the equation F = ma and know that the force and the acceleration are in the same direction

Describe, qualitatively, motion in a circular path due to a force perpendicular to the motion as: (a) speed increases if force increases, with mass and radius constant (b) radius decreases if force increases, with mass and speed constant (c) an increased mass requires an increased force to keep speed and radius constant mv 2 (F = is not required) r

Describe the moment of a force as a measure of its turning effect and give everyday examples

Define the moment of a force as moment = force × perpendicular distance from the pivot; recall and use this equation

Apply the principle of moments to situations with one force each side of the pivot, including balancing of a beam

State that, when there is no resultant force and no resultant moment, an object is in equilibrium

Apply the principle of moments to other situations, including those with more than one force each side of the pivot

Describe an experiment to demonstrate that there is no resultant moment on an object in equilibrium

State what is meant by centre of gravity

Describe an experiment to determine the position of the centre of gravity of an irregularly shaped plane lamina

Describe, qualitatively, the effect of the position of the centre of gravity on the stability of simple objects

Define pressure as force per unit area; recall and use the equation F p = A

Describe how pressure varies with force and area in the context of everyday examples

Describe, qualitatively, how the pressure beneath the surface of a liquid changes with depth and density of the liquid

Recall and use the equation for the change in pressure beneath the surface of a liquid ∆p = ρg∆h