Hooke’s Law + Terminal Velocity

Weight

The force acting on an object due to gravity

Mass

The amount of matter in an object

Gravitational field strength

The force per unit mass acting on an object

Weight equation

Weight = mass x gravitational field strength

Units of weight

Newtons (N)

Units of mass

Kilograms (kg)

Units of gravitational field strength

N/kg

Forces on a falling object

Weight acts downward and air resistance acts upward

Air resistance

A force that opposes motion through air

Resultant force

The overall force acting on an object

Acceleration of a falling object

Occurs when weight is greater than air resistance

Terminal velocity

The constant maximum speed reached by a falling object

Why terminal velocity is reached

Air resistance increases until it equals weight

Resultant force at terminal velocity

Zero

Motion at terminal velocity

Object moves at constant speed

Hooke’s Law

The extension of a spring is proportional to the applied force, up to the limit of proportionality.

Hooke’s Law equation

Force=spring constant x extension f=kxe

Spring constant

A measure of how stiff a spring is

Units of spring constant

N/m

Limit of proportionality

Point where the graph stops being straight

Elastic behaviour

Ability of a material to return to its original shape after deformation

Elastic deformation

Deformation that is reversible

Inelastic deformation

Deformation that is permanent

Equipment for Hooke’s Law practical

Spring, ruler, clamp stand and masses

Method of Hooke’s Law practical

• Attach a spring to a clamp stand and place a metre ruler vertically next to it, securing the ruler so it does not move.

• Measure and record the original length of the spring with no load, making sure to read the ruler at eye level

• Add a mass to the spring and record the new length. Calculate the extension by subtracting the original length from the new length.

• Repeat this process, adding further masses one at a time, ensuring the spring is not stretched beyond its limit of proportionality.

• Plot a graph of force (weight = mg) against extension and determine whether the graph is a straight line through the origin.

• AMACRP

Conclusion of Hooke’s Law practical

Extension increases proportionally with force in the linear region