4 - Forces in action

Question 1

What is Newton’s 2nd Law?

Answer 1

F = ma.

Question 2

Define geometric centre.

Answer 2

Middle of an object.

Question 3

Where is the centre of mass of an object of uniform density?

Answer 3

Geometric centre of the object.

Question 4

Why is the centre of mass higher than the geometric centre of a human?

Answer 4

Head more massive than feet.

Question 5

What happens when a force is applied to an object’s centre of mass?

Answer 5

Straight line motion produced without rotation.

Question 6

What is the centre of mass equal to?

Answer 6

The centre of gravity.

Question 7

How do you find an object’s centre of gravity?

Answer 7

.Suspend another object that comes to rest in line with the centre of gravity.
.Use plumb-bob and trace line on the object.
.Rotate object and trace plumb-line again.
.Centre of gravity is where the lines intercept.

Question 8

Define weight.

Answer 8

Gravitational force through centre of mass.

Question 9

Define friction.

Answer 9

2 surfaces rub against one another.

Question 10

Define drag.

Answer 10

Resistive force when travelling through a fluid.

Question 11

Define tension.

Answer 11

Stretched cable or rope.

Question 12

Define Upthrust.

Answer 12

Upward buoyancy in a fluid.

Question 13

Define normal contact force.

Answer 13

One object rests against another.

Question 14

What is responsible for acceleration down a slope?

Answer 14

Weight down a slope.

Question 14

Why do objects experience drag force?

Answer 14

Object colliding with particles in the fluid (liquid or gas).

Question 15

What factors increase drag on an object?

Answer 15

Cross-sectional area and velocity.

Question 16

What is the relationship between drag and speed?

Answer 16

Drag proportional to speed^2.

Question 17

What happens to drag as an object falls?

Answer 17

.g stays the same.
.No drag at t=0.
.Speed and drag increase until it balances with mg, then the object is at terminal velocity.

Question 18

Define moment.

Answer 18

Turning effect about some axis or point - clockwise or anticlockwise. Need a pivot, force and distance.

Question 19

What does it mean when a body is in equilibrium?

Answer 19

.Net forces/moments are 0.
.Not accelerating.
.Not rotating - clockwise = anti-clockwise.

Question 20

What is the equation for a moment?

Answer 20

Force x perpendicular distance of the line of action of force from the axis or point of rotation.
M = Fx.

Question 21

What if force and distance aren’t perpendicular?

Answer 21

Look in folder.

Question 22

What happens when something is in static equilibrium?

Answer 22

.Moments at any point are equal.
.If B is unknown, pick A so it’s contribution is 0.
.

Question 23

What happens if a force is applied anywhere but the centre of gravity?

Answer 23

It will rotate with translational motion (through space).

Question 24

How do you stop an object from rotating with translational motion?

Answer 24

Apply equal and opposite forces to it.

Question 25

Define couple.

Answer 25

Forces that produce rotational motion and no translational motion.

Question 26

Define torque.

Answer 26

The moment of a couple.

Question 27

How do you calculate torque?

Answer 27

One force x perpendicular separation between forces.

Question 28

How do you get a triangle of forces?

Answer 28

.Split force horizontally and vertically. .Make a triangle. .Tsin0 = W. .Tcos0 = F.

Question 29

What is the equation for density?

Answer 29

Density = mass/volume.

Question 30

What is the equation for pressure?

Answer 30

Pressure = Force/area.

Question 31

Define density.

Answer 31

How much mass per unit of volume.

Question 32

What is the relationship between density, mass and volume?

Answer 32

Mass and density directly proportional. Volume and density inversely proportional.

Question 33

What is 1cm^3 in m^3?

Answer 33

1 x 10^-6 m^3.

Question 34

What is the average weight of a human?

Answer 34

70kg.

Question 35

How do you work out the density of regular and irregular shapes?

Answer 35

.Measure mass on balance. .Regular - Measure dimensions with a Calliper/Micrometer/ruler .Irregular - displacement of liquid.

Question 36

What is the pressure exerted by the Earth's atmosphere?

Answer 36

1 x 10^5 Pa.

Question 37

What is the relationship between pressure, force and area?

Answer 37

Force and pressure directly proportional. Area and pressure inversely proportional.

Question 38

How is pressure exerted by a fluid?

Answer 38

Molecules are in constant, random motion and collide with each other and the walls of the container, producing a pressure.

Question 39

What is the equation for pressure of a liquid?

Answer 39

.P = m/v so m = pv so W = pVg .v = hA so W = PhAg p= F/A so p = W/a so phAg/a .p = hpg.

Question 40

What is the equation for the difference in force experienced at the top and at the bottom of an object?

Answer 40

xpgA. Upthrust = Axpg.

Question 41

Define Archimedes' Principle.

Answer 41

The upthrust exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces.

Question 42

For a floating object, what is it's upthrust equal to?

Answer 42

It's weight.

Question 43

How do you measure terminal velocity?

Answer 43

Look in folder.