Module 4

Question 1

Name an equation linking force, mass and acceleration

Answer 1

Net force = mass * acceleration

Question 2

Define mass and weight

Answer 2

Mass - Constant for a specific object or particle, not dependant on gravity

Weight - Variable magnitude; dependant on your position in the universe and the gravitational field strength

Question 3

Define Centre of Gravity

Answer 3

It is an imaginary point on an object where all of the weight acts

Question 4

Name 4 factors that affect the magnitude of drag forces

Answer 4

The speed of the object

The shape/surface area of the object

The texture of the object

The density of the fluid the object travels through

Question 5

What is the relationship between drag and speed?

Answer 5

Drag is proportional to the speed squared

Question 6

What is terminal velocity?

Answer 6

The point where an object is no longer accelerating - as theweight is equal and opposite to the drag force, so the object falls at a constant velocity

Question 7

What is the definition of a moment?

Answer 7

Moment = force * perpendicular distance of the line of action of the force from a pivot

Question 8

Give two conditions that must be met for an object to be considered to be in equilibrium

Answer 8

The net force must equal 0

The sum of the anticlockwise moments must equal the sum of the clockwise moments (or ƮƩ_acw = ƮƩ_cw)

Question 9

Define a couple

Answer 9

A couple is a pair of equal and opposite forces, that, when applied to an object, only produce rotational motion

Question 10

What is a Torque of a Couple?

Answer 10

A torque is a moment of a couple, where the forces are equal and opposite to each other, and the perpendicular distance between the force and the object is the same.

Torque = (F*0.5d)+(F*0.5d)

OR Torque of a Couple = one of the forces * perpendicular seperation between the forces

Question 11

Give the formula for density (ρ)

Answer 11

Density = mass / volume

Question 12

How can you determine the density of irregular solids?

Answer 12

By using diplacement - place the object in a measuring cylinder of water, and measure the volume of the water diplaced. This can then give density using ρ=m/V

Question 13

Give the formula for pressure

Answer 13

Pressure = Force / Area

Question 14

Define a fluid

Answer 14

Any substance that can flow (i.e. liquid or gas)

Question 15

Give a formula for finding pressure exerted by a liquid

Answer 15

P = hρg

Pressure = Height of liquid * density of the liquid * g

Question 16

Give a condition for floating, and a condition for sinking

Answer 16

For an object to float, ρ_solid < ρ_liquid

For an object to sink, ρ_solid > ρ_liquid

Question 17

What is pressure proportional to?

Answer 17

Pressure is proportional to height, meaning pressure increases with depth

Question 18

Give an equation to find upthrust

Answer 18

Upthrust = Axρg

Upthrust = Volume of solid * Density of liquid * g

Question 19

State Archimedies’ Principle

Answer 19

Upthrust exerted on a body fully or partially immersed in a fluid is equal to the weight of the fluid diplaced