Lesson 5: Forces and Elasticity

Question 1

How many forces do we need to apply to a stationary object to change the shape of the object (by either: stretching, bending or compressing?)

Answer 1

• More than one force has to be applied.
• If you apply only one force to a stationary object, then the forces on the stationary object are no longer balanced.
• So, the object will move rather than changing shape.

Question 2

What is the difference between elastic and inelastic deformation caused by stretching forces?

Answer 2

• Elastic deformation: When elastic materials will always return to their original length or shape if we take away the forces acting on them.
• Inelastic deformation: When inelastic materials don’t return to their original length when the forces are removed.

Question 3

What is the equation linking force, spring constant and extension?

Answer 3

Force = spring constant x extension
Spring constant: N/m.
extension m

Question 4

What is the equation that links elastic potential energy, spring constant and extension?

Answer 4

Elastic potential energy = 1/2 x spring constant x extension²

Question 5

Fill in the gaps

The ……… of an elastic object is ……….. ………… to the force applied, provided that the limit of proportionality is not exceeded.

Answer 5

• Extension
• Directly proportional

Question 6

What is the ONE case where the extension of a spring will not be directly proportional to the force applied on the spring?

Answer 6

• When the spring has reached its limit of proportionality (no longer behaves as an elastic material - won’t return to its original length.)

Question 7

What does a force that stretches/ compresses a spring do to the spring?

Answer 7

• It does work on the spring.
• Elastic potential energy will be stored in the spring (due to the work done on the spring.)

Question 8

Fill in the graps.

Provided the spring is not inelestically deformed, the ….. done on the spring and the ……. …….. …….. stored are equal.

Answer 8

• work
• elastic potential energy

Question 9

What is the ONE case where the work done on a spring (due to a force acting on it) will NOT be equal to the elastic potential energy stored in the spring?

Answer 9

• When the spring is inelastically deformed (when forces are released / removed from the spring, the spring doesn’t return to its original shape.)

Question 10

What is the difference betwen a linear and non- linear relationship between force (acting on a spring) and the extension of the spring?

Answer 10

• Linear: as one increases the other increases at the same rate (directly proportional - straight line.)
• Non- linear: as one increases, the other DOESN’T increase at the same rate (curved line.)

Question 11

What are the forces involved in stretching an object?

Answer 11

• Two pulling forces (equal and opposite.)

Question 12

What are the forces involved in compressing an object?

Answer 12

• Two pushing forces (equal and opposite.)

Question 13

What are the forces involved in bending an object?

Answer 13

• 3 forces
• Can be push/ pull forces.