Chapter 6 - Materials, newtons laws and momentum

Question 1

Hooke’s Law with equation.

Answer 1

for a material within it’s elastic limit, the force applied is directly proportional to the extension of the material.
- F = kx where k is the force constant of the material

Question 2

How to determine force constant

Answer 2

• Plot a force extension graph

- gradient is the constant

Question 3

Elastic deformation

Answer 3

When the force applied is removed, the material will return to it’s original shape/length, so the loading and unloading curves are the same (apart from rubber)

Question 4

Plastic deformation

Answer 4

When the force applied is removed, the material will not return to it’s original shape/length, so the loading and unloading curves are different

Question 5

Why is rubber special

Answer 5

• Does not experience plastic deformation but does not obey Hooke’s law, loading and unloading curves form hysteresis loop.

Question 6

Why is polythene special

Answer 6

• Does not obey Hooke’s law and experiences plastic deformation whenever any force is applied, so blue tac.

Question 7

How to calculate energy required to stretch the material out

Answer 7

Area between loading and unloading curves, or if loading = unloading E = 1/2kx^2

Question 8

Force constant of wires in series —|—

Answer 8

1/k1 + 1/k2 = 1/ktotal

Question 9

Force constant of springs in parallel |===|

Answer 9

k1 + k2 = ktotal

Question 10

What happens to work done if there is plastic deformation

Answer 10

instead of the work done being the energy stored as elastic potential, when plastic deformation occurs, the work is done in rearranging the atoms to form the new shape.

Question 11

Define tensile stress

Answer 11

Force applied to a material per cross sectional area, stress = F/A

Question 12

Define tensile strain

Answer 12

Extension or compression of a material per unit length, x/L

Question 13

Define youngs modulus

Answer 13

Ratio of stress to strain, and measures the stiffness of a material

Question 14

Define ultimate tensile strength

Answer 14

the maximum breaking stress that can be applied to a material

Question 15

Outline limit of proportionality

Answer 15

Up until this point Hooke’s law is obeyed

Question 16

Outline elastic limit

Answer 16

Beyond this point the material will experience plastic deformation

Question 17

Newtons First Law

Answer 17

an object will remain at rest or continue to travel with constant velocity unless acted upon by a resultant force

Question 18

Newtons second Law

Answer 18

F=ma

Question 19

Newtons third law

Answer 19

For every force on an object, there is an force equal in magnitude and opposite in direction

Question 20

What are the four fundamental forces

Answer 20

gravitational, electromagnetic, strong nuclear and weak nuclear

Question 21

Linear momentum

Answer 21

p = mv

Question 22

momentum a scalar or vector?

Answer 22

Vector

Question 23

Impulse of a force

Answer 23

measures the change in momentum, I = Ft

Question 24

area under force time graph

Answer 24

impulse

Question 25

Conservation of momentum

Answer 25

for a system of interacting objects, the total momentum in a specified direction remains constant, as long as no external forces act on the system

Question 26

Elastic collision

Answer 26

Kinetic energy is conserved

Question 27

Inelastic collision

Answer 27

Some of the kinetic energy is lost to other forms, such as heat or sound.

Question 28

One dimensional collision equation

Answer 28

m1u1 + m2u2 = m1v1 + m2v2

Question 29

Two dimensional collision

Answer 29

x direction: m1v0 = m1v1cosθ1 + m2v2cosθ2

y direction: 0 = mqv1sinθ1 + m2v2sinθ2