Chapter 4 - Force, Mass And Weight

Question 1

What is mass ?

Answer 1

The mass of an object is one of its physical properties and it depends on the amount of matter it contains

Question 2

What happens if a resultant (net) force acts on a object ?

Answer 2

A resultant force acting on a object will make he object accelerate in the direction of the resultant force.

Question 3

What’s the equation for net force ?

Answer 3

Force = mass x acceleration

Question 4

What’s force measured in ?

Answer 4

N

Question 5

What’s mass measured in ?

Answer 5

Kg

Question 6

What’s acceleration measured in ?

Answer 6

ms-2

Question 7

What does weight mean ?

Answer 7

The weight of an object on the surface of earth is the gravitational force acting on it

Question 8

What’s the SI unit for weight ?

Answer 8

Kgms-2

Question 9

What’s the equation for weight ?

Answer 9

W = mg

Question 10

What’s the acceleration of an object in free fall ?

Answer 10

9.81 ms-2

Question 11

What is friction ?

Answer 11

The force that arises when two surfaces rub against each other

Question 12

What is drag ?

Answer 12

The resistive force on an object travelling through a fluid, the same as friction

Question 13

What is tension ?

Answer 13

The force within a stretched cable or rope

Question 14

What is upthrust ?

Answer 14

An upward buoyancy force acting on a object when it is in a fluid

Question 15

What is a normal contact force ?

Answer 15

A force arising when one object rests against another object

Question 16

What does a object that is moving through a fluid experience ?

Answer 16

It experiences a drag force from the liquid and drag is a frictional force that opposes the motion of the object

Question 17

What contributes to the magnitude of a drag force ?

Answer 17

The magnitude of a drag force depends on several factors: speed of the object, shape of the object, the roughness/texture of the object and the density through which it travels.

The 2 most important factors that affect the magnitude of the drag force are the speed of the object and its cross-sectional area

Large cross sectional areas result in a greater drag force

Question 18

For most objects, drag force is directly proportional to …

Answer 18

Speed squared

For e.g. if the speed is doubled then the drag force would increase by a factor of 4 and if the speed was tripled then the drag force would increase by a factor of 9

Question 19

The drag force experienced by objects moving in the air is called …

Answer 19

Air resistance

Question 20

What do lots of modern vehicles have to reduce drag ? And what does it do ?

Answer 20

Modern vehicles have smooth, streamlined shapes to reduce air resistance exerted against them while they are travelling. This increases the top speed of the vehicle and also reduces the amount of fuel used on a journey

Question 21

During a vertical fall through air or another fluid, what happens to the weight of the object ?

Answer 21

the weight of the object stays constant

Question 22

During a vertical fall through air or another fluid, what happens to the drag force as the speed of the object increases ?

Answer 22

The drag force increases as the speed of the object increases

Question 23

What happens to the drag force the instant an object starts to fall ?

Answer 23

At the instant an object falls, there is no drag force on the object. The total drag force is equal to the weight.

Question 24

What happens as the object falls?

Answer 24

As the object falls, the speed increases and this in turn increases the magnitude of the opposing drag force. The resultant force on the object also decreases and after a while the object will reach terminal velocity

Question 25

What is terminal velocity ?

Answer 25

It is when the drag force on the object is equal and opposite to the weight. At terminal velocity, the object has zero acceleration and its speed is constant

Question 26

Whats the full velocity time graph for a object falling through the air ?

Answer 26

The instant the object starts to fall, there is no drag force on the object and the object accelerates. as the object falls, the speed increases so the opposing drag force also increases. Eventually the object reaches terminal velocity - when. The drag force is equal/opposite to weight and the objects speed is constant and the acceleration of the object is zero

Question 27

What’s a moment ?

Answer 27

A moment is the turning effect of a force

Question 28

Whats the equation for a moment ?

Answer 28

Moment = force x perpendicular distance from the pivot

Question 29

What will a moment act around ?

Answer 29

A moment will act around a pivot and a moment can act clockwise and anti-clockwise

Question 30

Whats a moment measured in

Answer 30

Nm

Question 31

Whats equilibrium ?

Answer 31

If we add up all the forces acting on a object and the resultant force is zero then the object is in equilibrium

Question 32

F1 x d1 =

Answer 32

F2 x d2

Question 33

What is a couple ?

Answer 33

A couple is defined as two equal and opposite forces acting on a body but on different lines of action.

The moment of a couple = force × perpendicular distance between the line of action of the forces

Question 34

What must happen in order for an object to be stable ? And what can you do to improve stability ?

Answer 34

In order for an object to be stable, the centre of mass must be over it’s base

To improve your stability:
- widen the base
- lower the centre of mass

Question 35

Torque means…

Answer 35

Turning force

Question 36

What’s density ?

Answer 36

Density is the mass of a substance for a given volume

Question 37

What type of property is density ?

Answer 37

Density is an intrinsic property - It is the same value for all objects made of that material

Question 38

1ml =

Answer 38

1cm 3

Question 39

What’s 1m2 in cm 2

Answer 39

10,000cm2

Question 40

What’s 1m3 in cm3 ?

Answer 40

1,000,000 cm3