Module 3 Springs & Hooke's law

Question 1

What are tensile forces?

Answer 1

forces pulling, aka tension

Question 2

What are compressing forces?

Answer 2

forces compressing an object

Question 3

Define Hooke’s Law

Answer 3

The extension is directly proportional to the force exerted below the elastic limit

Question 4

Formula for Hooke’s Law?

Answer 4

F=kx

F Force/N
k force or spring constant Nm^-1
x extension /m

Question 5

What is the symbol for springs constant?

Answer 5

k

Question 6

Another word for spring constant?

Answer 6

force constant

Question 7

What is the shape of a force extension graph for a material that obeys Hooke’s law?

Answer 7

straight line through the origin

Question 8

What does the gradient of a force extension graph equal?

Answer 8

the spring constant of the object k

Question 9

What does the spring constant represent?

Answer 9

how easy or hard it is to deform an object (larger the constant the harder it is to deform)

Question 10

Units for spring constant?

Answer 10

Nm^-1

Question 11

What is extension?

Answer 11

Extended length - Original length

Question 12

How is original length expressed?

Answer 12

L0 (measured with no mass)

Question 13

Formula for extension? (the one using lengths)

Answer 13

x = L - L0

Question 14

What is the elastic limit?

Answer 14

The maximum force a material can withstand without permanent deformation

Question 15

What happens below the elastic limit if a spring is unloaded?

Answer 15

spring returns to original length

Question 16

Describe how the shape of a force extension graph when a spring is loaded above its elastic limit?

Answer 16

graph becomes more flat and curved

Question 17

What part of a force extension graph must be used to calculate the spring constant?

Answer 17

straight part/linear part

Question 18

What happens when a weight is unloaded from a spring above the elastic limit?

Answer 18

permanent extension is observed in the spring
does not return to original length

Question 19

Describe the setup/apparatus used to find the spring constant?

Answer 19

Clampstand with a clamp attached to the object being measured

Attach a ruler to clamp so it is vertical and parallel to the object being tested

Attach weights to the object being measured and use a fiducial marker or a set square to read ruler

Question 20

What is a fiducial marker?

Answer 20

A pin of sorts which is hung on the bottom of a weight which allows measurements of distance to be taken more accurately

Question 21

Describe ways in which measurements of extension can be taken more accurately

Answer 21

using a fiducial marker or a set square at eye level

Question 22

Describe a method to find a spring constant of a spring, include how you would improve accuracy of your measurements

Answer 22

Measure original length of spring when no load is applied using a mm ruler clapped to a stand

Take readings at eye level using a fiducial marker to increase accuracy

Add lowest weight to the spring, once the spring is at rest record the new length of the spring

Use x=L-L0 to find extension

Measure mass of the weight using an electronic balance to, find weight by using mg

Repeat measurements at least 6 times with different weights

Plot a force extension graph using the results. Draw a line of best fit.

Gradient of the linear section is the force/spring constant

Question 23

How to add spring constants for springs in series?

Answer 23

same as adding resistances in parallel (think inverse)

Question 24

How to add spring constants for springs in parallel?

Answer 24

add them

Question 25

How will the gradients of a single spring, two identical springs in series, and in parallel compare in gradients?

Answer 25

Take k as gradient for individual spring
Series will be 0.5k
Parallel will be 2k

Question 26

Explain why the force constant will be given by 2k when two springs of force constant k are connected in parallel

Answer 26

F=kx
x is halved so k must double for same force

Question 27

What does the area underneath a force extension graph?

Answer 27

(elastic potential) energy

Question 28

Explain how the formula work done = 1/2kx^2
is derived?

Answer 28

Area under graph = 1/2Fx

F=kx

Plug this into the first equation

Question 29

Explain why when using Fx to find elastic potential energy in a loaded spring, 1/2 must be used?

Answer 29

it’s an average - think a plot of these values, it’s not a square it’s a triangle on force extension graph

Question 30

Why can the elastic energy stored in a spring not be directly linked to 1/2mv^2 in vertical motion?

Answer 30

GPE is not included

Three types of energy KE, EPE, GPE