WTMA Springs and Elasticity 5 — Questions and Answers
Question 1: If more coils are added to a coil spring while keeping the wire diameter and coil diameter the same, the spring becomes:
- Stiffer
- More flexible (Correct answer)
- Stronger
- Shorter
Correct answer: More flexible
More active coils means more material available to flex, reducing the spring constant and making the spring easier to deflect.
Question 2: If the wire diameter of a coil spring is doubled (keeping coil diameter and number of coils the same), the spring becomes:
- Much softer
- Slightly softer
- Much stiffer (Correct answer)
- Unchanged in stiffness
Correct answer: Much stiffer
Spring stiffness increases with the fourth power of wire diameter, so doubling the wire diameter makes the spring about 16 times stiffer.
Question 3: Both a rubber band and a steel spring return to their original shape after being stretched. This shared property is called:
- Plasticity
- Elasticity (Correct answer)
- Ductility
- Malleability
Correct answer: Elasticity
Elasticity is the ability of a material to return to its original shape after a deforming force is removed.
Question 4: If all dimensions are identical, which material would produce the stiffest spring?
- Rubber
- Aluminum
- Mild steel
- High-carbon steel (Correct answer)
Correct answer: High-carbon steel
High-carbon steel has the highest modulus of rigidity among these options, making springs from it the stiffest.
Question 5: Three springs, each with k = 30 lb/in, are connected in parallel and a 90-lb load is applied. How much does the assembly compress?
- 1 inch (Correct answer)
- 3 inches
- 9 inches
- 30 inches
Correct answer: 1 inch
Parallel total k = 30 + 30 + 30 = 90 lb/in; deflection = 90 lb / 90 lb/in = 1 inch.
Question 6: A weight hanging on a spring bounces up and down. If you replace the weight with a heavier one, the bouncing frequency will:
- Increase
- Decrease (Correct answer)
- Stay the same
- Become zero immediately
Correct answer: Decrease
Greater mass lowers the natural frequency of oscillation because the heavier weight has more inertia to overcome each cycle.
Question 7: The elastic potential energy stored in a compressed spring is proportional to:
- The compression distance
- Twice the compression distance
- The square of the compression distance (Correct answer)
- The cube of the compression distance
Correct answer: The square of the compression distance
Elastic potential energy = ½kx², so it is proportional to the square of the deflection distance.
WTMA Springs and Elasticity 5
If more coils are added to a coil spring while keeping the wire diameter and coil diameter the same, the spring becomes: