Forces & Elasticity

• What must happen for stationary objects to change their shape?

  More than one force has to be applied
• How can the shape of an object change?

  By stretching, bending, compressing, or a combination of all three
• What is an example of compression?

  Placing a mass on top of a spring on a flat surface
• What are the two forces acting on a spring when a mass is placed on top of it?

  The weight of the mass and the reaction force from the surface
• What is an example of stretching?

  Placing a mass on the bottom of a vertically hanging spring
• What are the two forces acting on a spring when a mass is placed at the bottom of it?

  The weight of the mass and the tension in the spring
• What is an example of bending?

  A diving board bending when a swimmer stands at the far end

  
• What are the two forces acting on a diving board when a swimmer stands on one end?

  The weight of the swimmer and the reaction force from the block to the diving board

  
• How can bending be caused besides the weight of an object?

  By two forces acting at an angle to each other
• What is the difference between elastic and inelastic deformation?

  Elastic materials return to their original shape, while inelastic materials do not
• What is elastic deformation?

  When objects return to their original shape when the stretching force is removed
• Name examples of materials that undergo elastic deformation.

  Rubber bands, fabrics, and steel springs
• What is inelastic deformation?

  When objects remain stretched and do not return completely to their original shape
• Name examples of materials that undergo inelastic deformation.

  Plastic, clay, and glass
• What does Hooke's Law describe?

  The relationship between the extension of an elastic object and the applied force

  
• What does Hooke's Law state about extension and force?

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

  
• If the force applied to an elastic object is doubled, what happens to the extension?

  The extension will also double
• What is the limit of proportionality?

  The point beyond which the relationship between force and extension is no longer directly proportional

  
• What is the equation for Hooke's Law?

  F = k × e

  
• What do the symbols in the Hooke's Law equation represent?

  F = force in newtons, k = spring constant in N/m, e = extension in metres

  
• What does the spring constant represent?

  How stiff a spring is; a higher spring constant means a stiffer spring

  
• How can the extension of an object be calculated?

  By subtracting the original length from the final length
• What is the importance of unit conversions in Hooke's Law?

  Extension must be in metres when the spring constant is in N/m

  
• In the example of a child on a pogo stick, what is the spring constant?

  4900 N/m
• What is the weight of the child if the spring compresses from 40 cm to 33 cm?

  343 N
• What does a straight line on a force-extension graph indicate?

  The material obeys Hooke's law

  
• What does a curve on a force-extension graph indicate?

  The material does not obey Hooke's law

  
• What is the Hooke's law region on a force-extension graph?

  Where the graph is a straight line

  
• What does the symbol Δ represent in the context of force-extension graphs?

  It means 'change in' a variable
• What does the symbol '∝' mean in the context of Hooke's law?

  It means 'proportional to'

  
• How can the spring constant be calculated from Hooke's law?

  By rearranging the equation to k = F/e

  
• What does a larger spring constant indicate about a spring?

  It requires more force per unit extension

  
• What is the spring constant if a mass of 0.6 kg extends a spring by 2 cm?

  To be calculated using the weight of the mass and the extension

  
• What is the relationship between force and extension in a Hooke's law graph?

  Force is proportional to extension in the linear region

  
• What happens to materials beyond their limit of proportionality?

  They will have a non-linear relationship between force and extension

  
• Why is it important to understand Hooke's law graphs for exams?

  Hooke's law questions are very common in exams

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

  The spring constant of the material

  
• What is the significance of the limit of proportionality on a force-extension graph?

  It marks the transition from linear to non-linear behavior

  
• What is the unit for the spring constant?

  Newtons per metre (N/m)
• What does a straight line on a force-extension graph indicate about the material?

  The material obeys Hooke's law