MODULE 3: FORCES AND MOTION

Question 1

stopping distance

Answer 1

THINKING + BRAKING distance

Question 2

Center of mass

Answer 2

Point where external forces produce a straight line of motion with no rotation

Question 3

Center of gravity

Answer 3

Point where entire weight of object appears to act

Question 4

Experiment to find center of gravity

Answer 4

EQUIP: stand, paper, plumb line
EXPERIMENT: suspend paper freely using stand,
Use plumb line to draw a straight vertical line on the object
Rotate the object and do this again
Intersection = center of gravity

Question 5

What is drag?

Answer 5

Resistive forces when a object moves through a fluid

Question 6

What is a fluid?

Answer 6

Liquid or gas

Question 7

What is drag proportional to

Answer 7

Velocity squared

Question 8

What is terminal velocity

Answer 8

When drag is equal to weight, so Fres = 0.

Question 9

What is the moment of a force?

Answer 9

Product of force applied and the perpendicular distance of the line of action from the pivot .

Question 10

Moment equation

Answer 10

Moment = fx so newton meters

Question 11

What is the principle of moments

Answer 11

Sum of anti-clockwise moments is equal to the sum of clockwise moments about the same point OR axis

Question 12

Conditions for equilibrium

Answer 12

Fres is zero

Resultant Moment is zero

Question 13

What is a couple

Answer 13

Two forces equal in magnitude but opposite in direction

Question 14

What is the torque of a couple

Answer 14

Product of one of the forces (they are the same) and the perpendicular separation between them

Question 15

How is torque and moment related

Answer 15

Torque is the same as total moment of the two forces about the midpoint between the forces

Question 16

Density equation

Answer 16

ρ=mass / volume

Question 17

How to measure density

Answer 17

Measure mass using weighing scale
Measure volume, for regular measure using callipers each edge. For irregular solids find displaced volume using displacement can

Question 18

What is pressure

Answer 18

Normal force exerted on a surface. Pressure is force over cross sectional area

Question 19

What is Archimedes principle

Answer 19

The upthrust exerted on a body immersed in a fluid (partially or fully) is equal to the weight of the fluid that the body displaces

Question 20

What is pressure proportional to and how in a cylinder column

Answer 20

p = f/a
p = mg/a
mass = pressure x volume
p = (ρV)g/a
height = volume / cross section area (v/a)
p = hρg
g and ρ are constant in a cylinder column, p is proportional to the height of the column

Question 21

What is work done and equation

Answer 21

W = Fx cos theta
Work done is the energy transfer from one to kinetic. One joule is the energy which one joule has moved an object one meter

Question 22

Formula for GPE and KE

Answer 22

Ek = 1/2 mv^2
Ep = mgh

Question 23

What is power

Answer 23

Rate of work done, rate of energy transfer

Question 24

Power equation

Answer 24

P=W/t

Question 25

How does power relate to force

Answer 25

P = force x velocity | P=Fv

Question 26

Efficiency equation and what it is

Answer 26

Efficiency = useful energy / total energy It is a ratio between useful and total energy input or output Between 0 and 1

Question 27

Hooke law

Answer 27

The extension of a spring is directly proportional to the force applied

Question 28

Properties of plastic

Answer 28

Removal of force will not make object return to its original length

Question 29

Elastic properties

Answer 29

Removal of force makes it go back to its original shape

Question 30

Elastic potential equation

Answer 30

Ee = half Fx

Question 31

Elastic potential energy is proportional to what

Answer 31

extension squared F=is E=1/2 Fx so E = 1/2 k x^2

Question 32

Brittle properties

Answer 32

No deformation before break, they don’t bend they just snap

Question 33

Ductile properties

Answer 33

Can be stretched and bent and thinned without breaking

Question 34

What is tensile stress

Answer 34

Same as pressure, force per unit cross sectional area

Question 35

What is tensile strain

Answer 35

Ratio of extension to the original length.symbol epsilon

Question 36

What is Young’s modulus

Answer 36

Ratio of tensile stress against strain E = stress / strain

Question 37

What happens at the elastic limit for brittle vs rubber?

Answer 37

Brittle it snaps | Rubber has no limit

Question 38

How can the spring equation be put used with the Young’s modulus

Answer 38

E = stress/strain = (F/A)/(x/L) = Fl/Ax. E = Fl/Ax, F = EAX/L F = (EA/L)x, spring constant in F=kx is EA/L

Question 39

first law of motion

Answer 39

An object will remain at rest or continue to move with a constant velocity until a net resultant force acts upon it

Question 40

Third law of motion

Answer 40

Who two objects interact an equal and opposite force is always exerted, and a they are the same typr

Question 41

What is momentum

Answer 41

Product of mass and VELOCITY

Question 42

What is conservation of momentum

Answer 42

Closed system, total initial momentum is equal to the final momentum

Question 43

What is an elastic collision

Answer 43

Total KINETIC energy is equal after and before ( no transfer to other stores)

Question 44

Newton second law of motion

Answer 44

Net resultant force is directly proportional to the rate of change of momentum and is in the same direction

Question 45

What is the force equation in terms of linear momentum and what is the requirement

Answer 45

for a constant mass object | F = Δp/Δt, = (mv-mu)/Δt = m((v-u)/t) = ma, F = ma

Question 46

What is the impulse of a force

Answer 46

The product of force and time, and in terms of Newton’s laws it’s the change in momentum (so just momentum units)

Question 47

What’s the area under force t graph

Answer 47

Force x time = impulse (Δp)

Question 48

Impulse equation

Answer 48

I = change in momentum

Question 49

Final velocity and average velocity formula

Answer 49

FINAL = 2 * AV