Topic 4

Question 1

Force definition

Answer 1

any action that causes a change in motion or shape of body

Question 2

Properties of foce

Answer 2

line of action, magnitude, direction, point of application

Question 3

1st law of motion

Answer 3

law of inertia
“an object will remain at rest or in motion unless acted upon by an external force”

Question 4

2nd law of motion

Answer 4

law of acceleration
“the change in motion of an object is proportional to the force impressed; and is made in the direction of the straight line in which it is impressed”
high force = high acceleration
high mass = high force
low mass = high acceleration

Question 5

3rd law of motion

Answer 5

law of reaction
“for every action, there is an equal and opposite reaction”

Question 6

Force =

Answer 6

mass x acceleration

Question 7

mass

Answer 7

the amount of matter an object has.
Is constant regardless of where you are.
scalar quantity, measured in kg.we

Question 8

weight force

Answer 8

force experienced by an object due to gravity.
Weight = mass x acceleration due to gravity (9.81m/s)
vector quantity (always in the downward direction), measured in newtons

Question 9

Muscular forces

Answer 9

forces exerted at point of application (e.g. origin/insertion)

Question 10

Ground reaction forces

Answer 10

force exerted by the ground, on a body in contact with it

Question 11

joint reaction force

Answer 11

force generated within a joint in response to forces acting on a joint

Question 12

friction forces

Answer 12

force that arises whenever 1 body moves across the surface of another.

Question 13

Frictional force =

Answer 13

μ x Fn
Friction coefficient x Normal force

Question 14

Fn

Answer 14

normal force
= force acting perpendicular to the surface

Question 15

μ

Answer 15

friction coefficient.
a dimensionless value that varies with different surfaces.
a smooth surface = low μ
a rougher surface + high μ

Question 16

Surface area

Answer 16

Friction is independent of surface area
1. the areas in contact have no effect on friction
2. if load of object is doubled, its friction will also double

Question 17

Static friction

Answer 17

Limiting friction
max static friction generated between 2 surfaces just before the object begins to move.
frictional force required to overcome inertia

Question 18

dynamic friction

Answer 18

kinetic or sliding friction
friction generated by 2 surfaces in motion.
lower than static friction

Question 19

Fridge weight if mass is 120kg =

Answer 19

w = m x g
120 x 9.81 = 1177.2

Question 20

normal force if weight is 1177.2 =

Answer 20

on a flat surface Fn is equivalent to weight.
= 1177.2

Question 21

frictional force if μ is 0.5, and Fn is 1177.2 =

Answer 21

μ x Fn
0.5 x 1177.2 = 588.6N

Question 22

If frictional force of fridge is 588.6, how much force needs to be produced to move the object

Answer 22

> 588.6N is required to overcome inertia