Module 3 - Forces and Motion

What are some factors that could affect thinking distance?

Drug and alcohol use, tiredness, distractions

How do air bags and crumple zones reduce the impact force on a passenger?

They decrease the rate of change of momentum, reducing the impact force

Define weight

The gravitational force acting on an object through its centre of mass

Define friction

The force that arises when two non-smooth surfaces rub together

Define drag

The resistive force on an object moving through a fluid

Define tension

The force within a stretched rope or cable

Define upthrust

The upward buoyancy force acting on an object when it is in a fluid

Define normal contact force

The force that arises when an object rests on another object. It acts perpendicular to the plane of contact

Define terminal velocity

When the forces acting on a falling object become balanced so the resultant force is zero, therefore the acceleration is also zero, meaning the object has reached its maximum velocity

Define the principle of moments

For an object in equilibrium, the sum of the clockwise moments is equal to the sum of the anticlockwise moments

Define moment

A turning force

What is the equation for moment?

M = F* perpendicular distance

What is meant by a couple?

A pair of equal and opposite co-planar forces applied to a body parallel to each other but not along the same line

State Archimedes’ Principle

The upthrust exerted on a body immersed in a fluid is equal to the weight of the fluid that the body displaced. For sinking objects, the weight is greater than the upthrust but for floating objects, the weight and upthrust are equal

Define work done

Force x distance

Define kinetic energy and its base SI unit

The energy store associated with the motion of an object with mass. Unit kg m²/s²

What is extension of a spring?

Tensile forces act away from the centre of the spring in both directions and will stretch it out, causing it to extend, called tensile deformation

What is the compression of a spring?

Forces acting towards the centre of the spring in both directions causes compression, called compressive deformation

Define Hooke’s Law

The force applied to an object is directly proportional to the extension, up until the limit of proportionality

Define tensile stress

Ratio of a stretching force on a material to the material’s cross-sectional area

What is the equation for the Young’s modulus?

E=σ/ε; E is Young’s modulus; σ is tensile stress; ε is tensile strain

What is ultimate tensile strength?

The maximum amount of force a material can withstand before fracture

What is yield strength?

The maximum amount of force a material can withstand before undergoing plastic deformation

What does it mean when a material is necking?

A reduction in the cross-sectional area of the material under a tensile force

What is strain hardening?

The use of plastic deformation to increase the strength of the material

How can a material’s behaviour be graphically modelled?

With a stress-strain graph; stress on y-axis; strain on x-axis

Define a ductile material

Materials that can be drawn into wires and will show plastic deformation under tensile stress before fracture

Define a malleable material

A material that can be hammered into flat sheets and will show extensive plastic deformation under tensile stress

Define a brittle material

A material that breaks with little to no plastic deformation

Define a hard material

A material that will resist plastic deformation by surface indentation or scratching

Define the stiffness of a material

The ability for the material to resist tensile forces

Define a polymeric material

A material made of polymers