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 when a mass is placed on a vertically hanging spring?

  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 it?

  The weight of the swimmer and the reaction force from the block

  
• How can bending be caused?

  By two forces at an angle to each other or more than one force on an object
• What is elastic deformation?

  When objects return to their original shape when the stretching force is removed

  
• What are 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

  
• What are 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 is doubled, what happens to the extension according to Hooke's Law?

  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 (N), k = spring constant in N/m, e = extension in metres (m)

  
• 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 does the symbol e represent in Hooke's Law?

  It can represent either the extension or compression of an elastic object

  
• What is the significance of the Hooke's Law experiment?

  It tests the relationship between force and extension in elastic materials

  
• How do you calculate the weight of a child on a pogo stick using Hooke's Law?

  By using the equation F = ke, where k is the spring constant and e is the extension

  
• What is the spring constant of the pogo stick spring in the example?

  4900 N/m
• How do you calculate the extension of the pogo stick spring?

  By subtracting the final length from the original length
• What is the extension of the pogo stick spring if the original length is 40 cm and the final length is 33 cm?

  7 cm
• How do you convert the extension from centimeters to meters?

  By dividing by 100
• What is the weight of the child if the spring constant is 4900 N/m and the extension is 0.07 m?

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

  That the material obeys Hooke's law

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

  That the material does not obey Hooke's law

  
• What happens to materials beyond their limit of proportionality?

  They have a non-linear relationship between force and extension

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

  The part of the graph where the relationship is a straight line

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

  It means the '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 k = F/e

  
• What does a larger spring constant indicate?

  That more force is required per unit extension

  
• How do you calculate the force on a spring from a suspended mass?

  By calculating the weight of the mass using W = mg
• What is the gravitational field strength used in the example?

  1. 8 N/kg

  
• What is the weight of a mass of 0.6 kg?

  1. 88 N