Forces and Matter

What is required to stretch, bend or compress an elastic object such as a spring?

More than one force must act on the object.

What is elastic distortion?

A change in shape where the object returns to its original shape when the force is removed.

What is inelastic distortion?

A change in shape where the object does not return to its original shape when the force is removed.

What is the equation linking force, spring constant and extension?

F = k × x

What does F = k × x mean?

Force (N) = spring constant (N/m) × extension (m).

What is the spring constant?

A measure of how stiff a spring is; it is the force required per metre of extension.

What is the unit of spring constant?

N/m (newtons per metre).

What does a larger spring constant mean?

The spring is stiffer and requires more force to produce the same extension.

What is the equation for energy transferred when stretching a spring?

E = ½ × k × x²

What does E = ½kx² calculate?

The energy transferred or work done in stretching a spring, measured in joules.

What happens to the energy stored in a stretched spring?

It is stored as elastic potential energy.

What is a linear force-extension relationship?

An increase in force produces a directly proportional increase in extension, giving a straight-line graph through the origin.

What is a non-linear force-extension relationship?

Force and extension are not directly proportional, so the graph is curved.

What happens to a spring if it is stretched beyond its elastic limit?

It undergoes inelastic deformation and does not return fully to its original length.

What is the core practical for Topic 15?

Investigate the extension and work done when applying forces to a spring.

How can you investigate the extension of a spring?

Hang masses from a spring, measure its extension for different forces, and plot a force-extension graph.

How is extension calculated in the spring practical?

Extension = stretched length − original length.

Why should the initial length of the spring be measured?

To calculate the extension accurately for each applied force.

What does the gradient of a linear force-extension graph represent?

The spring constant, k, when force is plotted against extension.

Why should measurements be repeated in the spring practical?

To identify anomalous results and improve reliability.

Why does atmospheric pressure decrease with height?

There is less air above you at higher altitudes, so the weight of air pressing down is smaller.

What causes atmospheric pressure?

The weight of the air above a surface due to gravity.

What is fluid pressure?

Pressure produced by a fluid, including both the fluid's pressure and atmospheric pressure.

What direction does pressure in a fluid act on a surface?

Perpendicular (normal) to the surface.

How is pressure related to force and area?

For the same force, increasing the area decreases pressure; decreasing the area increases pressure.

What is the equation for pressure?

P = F ÷ A

What does P = F/A mean?

Pressure (Pa) = force normal to a surface (N) ÷ area of the surface (m²).

What is the unit of pressure?

Pascal (Pa).

What is 1 pascal equal to?

1 N/m².

Why does a sharp knife exert more pressure than a blunt knife?

The sharp knife has a smaller contact area, so the same force produces greater pressure.

Why do snowshoes reduce pressure on snow?

They increase the contact area, reducing the pressure on the snow.

How does pressure in a liquid change with depth?

Pressure increases as depth increases.

How does pressure in a liquid change with density?

For the same depth, pressure increases as the density of the liquid increases.

Why does liquid pressure increase with depth?

There is a greater column of liquid above the point, so the weight of the liquid above is greater.

What is the equation for pressure due to a column of liquid?

P = h × ρ × g

What does P = hρg mean?

Pressure due to a liquid (Pa) = height/depth of liquid (m) × density (kg/m³) × gravitational field strength (N/kg).

What factors determine the pressure due to a column of liquid?

The depth/height of the liquid, its density and gravitational field strength.

How do you calculate the difference in pressure between two depths in the same liquid?

Use ΔP = ρgΔh.

What is upthrust?

The upward force exerted by a fluid on an object immersed in it.

Why does a fluid exert an upthrust on an object?

Fluid pressure is greater at greater depths, producing a resultant upward force.

In what direction does upthrust act?

Upwards.

What does the upthrust on an object equal?

The weight of fluid displaced by the object.

What happens when an object is fully immersed in a fluid?

It displaces a volume of fluid equal to its own volume.

What happens when an object is partially immersed in a liquid?

It displaces a volume of liquid equal to the submerged volume of the object.

What determines whether an object floats or sinks?

The relative sizes of its weight and the upthrust, which depend partly on the object's density and the fluid's density.

When does an object sink?

Its weight is greater than the maximum upthrust acting on it.

When does an object float?

The upthrust balances its weight.

What happens to an object that is neutrally buoyant?

Its weight equals its upthrust and it remains suspended in the fluid.

How does fluid density affect floating?

A denser fluid provides greater upthrust for the same volume displaced, making floating easier.

Why can a steel ship float even though steel is denser than water?

The ship's hollow shape means its overall average density is less than water, allowing it to displace enough water for the upthrust to balance its weight.