Topic 15: Forces and Matter

• What must be applied to stretch, bend, or compress an object?

  More than one force
• What happens if a single force is applied to an object?

  The object moves in the force's direction
• What occurs when forces are applied inwards from opposite sides of a spring?

  The spring will compress
• What is a reaction force in the context of a spring?

  A force from the fixed point of the spring
• What does deformation mean?

  Changing shape
• What is elastic deformation?

  The object returns to its original shape
• Give an example of elastic deformation.

  An elastic band
• What is plastic deformation?

  The object does not return to its original shape
• Give an example of plastic deformation.

  A spring when pulled too far
• What does the spring constant \( k \) represent?

  Force required to extend a spring per metre
• What is Hooke's Law?

  The extension of a spring is proportional to force
• Write the formula for Hooke's Law.

  $F =$$kx$
• What does \( F \) represent in Hooke's Law?

  Force applied to the spring, N
• What does \( k \) represent in Hooke's Law?

  Spring constant, Nm⁻¹
• What does \( x \) represent in Hooke's Law?

  Extension, m
• What does a linear section on a Force/Extension graph indicate?

  It follows Hooke's Law and is elastic
• What is the gradient of the linear section on a Force/Extension graph?

  Spring constant \( k \)
• What is the elastic limit?

  The point where deformation stops being linear
• What happens beyond the elastic limit?

  The material does not obey Hooke's Law
• What characterizes a non-linear section on a Force/Extension graph?

  It indicates plastic deformation
• What does shallow non-linear deformation indicate?

  Lots of extension for little force
• What does a linear graph without non-linear sections indicate?

  The material is brittle and snaps
• What is the formula for work done in relation to a spring?

  $Work Done =$$\frac{1}{2}kx^2$
• What is atmospheric pressure?

  Total weight of air above a unit area
• How does atmospheric pressure change with altitude?

  It decreases with increasing height
• Why does atmospheric pressure decrease with height?

  Fewer air molecules above the unit area
• What is the relationship between pressure and the weight of air?

  Pressure is caused by the weight of air
• What is a fluid?

  A liquid or a gas
• What does the pressure of a gas depend on?

  Atmospheric pressure
• What happens if the inward force on a balloon exceeds the outward force?

  The balloon will collapse
• How does lower atmospheric pressure in space affect a balloon?

  The gas inside exerts greater outward force
• What happens when you blow into a balloon?

  Increases collisions and pressure inside
• What does pressure in a fluid cause?

  A force perpendicular to any surface
• How does pressure vary with depth in a fluid?

  Greater depth means greater pressure
• What causes greater pressure in a fluid?

  Greater amount of fluid above the object
• How does fluid density affect pressure?

  Greater density means greater pressure
• What is the formula for mass in relation to density and volume?

  $mass =$$density \times volume$
• What condition allows an object to float?

  Weight less than displaced water weight
• How does a boat float in water?

  It displaces its weight in water
• What is the buoyancy force?

  Upwards force counteracting the object's weight