Explain, using springs and other elastic objects, that stretching, bending or compressing an object requires more than one force

Describe the difference between elastic and inelastic distortion

Recall and use the equation for linear elastic distortion including calculating the spring constant:

force exerted on a spring (newton, N) = spring constant (newton per metre, N/m) × extension (metre, m)

\(F = k × x\)

Use the equation to calculate the work done in stretching a spring:

energy transferred in stretching (joules, J) = 0.5 × spring constant (newton per metre, N/m) × (extension (metre, m))²

\(E = \dfrac{1}{2} × k × x^2\)

Describe the difference between linear and non-linear relationships between force and extension

Core Practical: Investigate the extension and work done when applying forces to a spring

Explain why atmospheric pressure varies with height above the Earth’s surface with reference to a simple model of the Earth’s atmosphere

Describe the pressure in a fluid as being due to the fluid and atmospheric pressure

Recall that the pressure in fluids causes a force normal to any surface

Explain how pressure is related to force and area, using appropriate examples

Recall and use the equation:

pressure (pascal, Pa) = force normal to surface (newton, N) ÷ area of surface (square metre, m²)

\(P = \dfrac{F}{A}\)

Describe how pressure in fluids increases with depth and density

Explain why the pressure in liquids varies with density and depth

Use the equation to calculate the magnitude of the pressure in liquids and calculate the differences in pressure at different depths in a liquid:

pressure due to a column of liquid (pascal, Pa) = height of column (metre, m) × density of liquid (kilogram per cubic metre, kg/m³) × gravitational field strength (newton per kilogram, N/kg)

\(P = h × \rho × g\)

Explain why an object in a fluid is subject to an upwards force (upthrust) and relate this to examples including objects that are fully immersed in a fluid (liquid or gas) or partially immersed in a liquid

Recall that the upthrust is equal to the weight of fluid displaced

Explain how the factors (upthrust, weight, density of fluid) influence whether an object will float or sink