P2.3 (1) - forces in action

Question 1

what are elastic bodies?

Answer 1

objects that return to original shapes when the deforming force is removed

Question 2

what are plastic bodies?

Answer 2

objects that do not return to their original shape when the deforming force is removed

Question 3

state hooke’s law

Answer 3

the extension of a body is directly proportional to the force applied, as long as the limit of proportionality is not exceeded

Question 4

what is the equation for hooke’s law?

Answer 4

force = spring constant x extension 
(N)    =     (N/m)                 x  (m)

F = K x E

Question 5

how can the spring constant be found from a force-extension graph?

Answer 5

from the gradient

Question 6

where does the limit of proportionality lie on an extension-force graph?

Answer 6

just before it begins to curve

Question 7

what is the elastic limit?

Answer 7

the like middle point

• if exceeded, spring is permanently deformed (even when force is removed)
• below limit, spring returns to original length

Question 8

where is the elastic limit on a force-extension graph?

Answer 8

just after the limit of proportionality

Question 9

what is the spring constant a measure of?

Answer 9

the stiffness of a spring

Question 10

if a spring is very stiff, how is the spring constant?

Answer 10

higher

Question 11

what is the equation to figure out the work done while stretching a spring?

Answer 11

energy (J) = 0.5 x spring constant (N/m) x (extension (m))^2

Question 12

what is the work done while stretching a spring also known as?

Answer 12

elastic potential energy

Question 13

can you use an elastic band instead of a spring when using a newton-meter, and why?

Answer 13

no, as it does not obey Hooke’s law (as it has a non-linear relationship between force and extension)

Question 14

why is a rubber balloon hard to blow up at first (picture graph in your head)?

Answer 14

as rubber does not follow hooke’s law.

so at the beginning the gradient is very high, meaning more force is applied to increase its extension

Question 15

describe the relationship between glass and force and extension

Answer 15

it has a linear relationship (straight line), but a very steep gradient - as it is a stiff material

Question 16

what prevents tennis rackets from being deformed when hitting a tennis ball?

Answer 16

they are specially designed to transfer energy back, rather than storing them when they deform

Question 17

what causes materials to deform?

Answer 17

storing too much energy

Question 18

what is elastic potential energy?

Answer 18

energy stored by an elastic body (that has been stretched)

Question 19

how is a rubber band able to revert back to its original shape when the force is released? (energy)

Answer 19

converts elastic potential energy to kinetic energy (and so it moves)

Question 20

define a field

Answer 20

a region of space within which a body experiences a force

Question 21

where would you find a gravitational field?

Answer 21

around anything with mass (infinite)

Question 22

where would you find a magnetic field?

Answer 22

around any magnet

Question 23

where would you find an electrostatic field?

Answer 23

around anything that is charged

Question 24

do fields exert the same force on every body?

Answer 24

no, it depends on how much mass/charge/magnetism the body itself has

Question 25

what is the unit for gravity?

Answer 25

n/kg

Question 26

what is weight?

Answer 26

The force of the Earth on an object (acts downwards)

Question 27

what is gravitational field strength a measure of?

Answer 27

the force on 1kg of mass in a gravitational field (due to another mass)

Question 28

what is the equation to calculate gravity constant?

Answer 28

mass x gravitational field strength

Question 29

what is gravitational potential energy?

Answer 29

The energy transferred to a gravity store when you lift an object in a gravitational field

Question 30

equation for calculating gravitational potential energy

Answer 30

(J) = mass (kg) x height (m) x gravitational field strength (N/kg)

Question 31

what has to be present to stretch, bend or compress an object?

Answer 31

more than one force must be present + applied

Question 32

what is the difference between linear and non-linear relationship between force and extension?

Answer 32

linear relationships obey hooke’s law, non-linear relationships do not obey hooke’s law

Question 33

how would a gravitational field differ with mass?

Answer 33

greater the mass, greater the gravitational field around it

Question 34

what is the acceleration in free fall?

Answer 34

10m/s^2