Forces

Question 1

What happens to the energy in a car when it slows down?

Answer 1

When a car slows down, energy is transferred from the kinetic energy store of the car to the thermal energy store of the brake pads and brake discs.
Friction between the car’s brake pads and brake discs does mechanical work to oppose the car’s motion.
The work done by the force of friction, given by the equation Work = force x distance
This mechanical work converts the car’s kinetic energy into thermal energy.
As a result, the brake pads and brake discs heat up as energy has been transferred to its thermal energy store.

Question 2

What are factors affecting thinking distance?

Answer 2

Condition of driver - tiredness, alcohol, drugs, mobile phone, raction time
Speed - faster the car is moving, the further it will go while the driver is reacting

Question 3

What are the factors affecting braking distance?

Answer 3

Condition of the road (wet, dry etc.)
Condition of the tyres - new, worn (old tyres increase breaking distance
condition of brakes
force exerted by the brakes
mass of the car
speed of car

Question 5

What is a force?

Answer 5

A push or pull that acts on an object due to the interaction with another object.

Question 6

What are the two types of forces?

Answer 6

• Contact forces
• Non-contact forces

Question 7

What are examples of contact forces?

Answer 7

• Friction
• Air resistance
• Tension
• Normal contact force

Question 8

What are examples of non-contact forces?

Answer 8

• Gravitational force
• Electrostatic force
• Magnetic force

Question 9

Is force a scalar or vector quantity?

Answer 9

Vector quantity.

Question 10

Students should be able to describe the interaction between pairs of objects which produce a force on each object. True or False?

Answer 10

True

Question 11

How should forces be represented?

Answer 11

As vectors.

Question 12

What is weight? What does weight depend on?

Answer 12

Weight is the force acting on an object due to gravity. The force of gravity close to the earth is due to the gravitational field around the earth.

The weight of an object depends on the gravitational field strength at the point where the object is.

Question 13

What is the atmosphere?

Answer 13

A thin layer of air around the Earth

Question 14

How does the density of the atmosphere change with altitude?

Answer 14

It gets less dense with increasing altitude

Question 15

What creates atmospheric pressure?

Answer 15

Air molecules colliding with a surface

Question 16

How does the number of air molecules above a surface change with height?

Answer 16

It decreases as the height of the surface increases

Question 17

What happens to atmospheric pressure as height increases?

Answer 17

It decreases

Question 18

Fill in the blank: The atmosphere is a _______ layer of air round the Earth.

Answer 18

thin

Question 19

True or False: Atmospheric pressure increases with altitude.

Answer 19

False

Question 20

What are the typical values for someone walking, running or cycling?

Answer 20

walking - 1.5m/s
running - 3 m/s
cycling - 6m/s

Question 21

What does Newton’s 1st law state?

Answer 21

If the forces acting on an object are balanced, the resultant force on the object is 0, then
if the object is stationary, it will remain stationary
and if the object is moving, it will continue to move at a constant velocity

Question 22

What is inertia?

Answer 22

Inertia is the tendency of object to continure in their state of rest or uniform motion.W

Question 23

What does Newton’s second law state?

Answer 23

The acceleration of an object is proportional to the resultant force acting on the object, and inversely proportional to the mass of the object.
Equation:
force = mass x acceleration
f = ma

Question 24

What is inertial mass?

Answer 24

nertial mass is a measure of how difficult it is to change thevelocity of an object
inertial mass is defined as the ratio of force over acceleration.

Question 25

What does Newton’s 3rd law state?

Answer 25

Whenever 2 objects interact with each other, the forces they exert on each other are equal in magnitude and opposite in direction:
if object A exerts a force on object B, then object B exerts a force on object A and those forces are equal in magnitude and opposite in direction.

Question 26

What are the resistive forces in solids, liquids and gases?

Answer 26

Solids:
Friction

Liquids:
drag

Gas:
drag
air resistance

Question 27

What does magnitude of the resistive force depend on?

Answer 27

It depends on the object’s:
surface area
speed - the greater the speed, the greater the air resistance
shape
surface roughness

Question 28

What is terminal velocity?

Answer 28

Terminal velocity is the maximum velocity attainable by an object as it falls through a fluid (e.g air)

Question 29

A skydiver is falling. Explain her motion in terms of forces.

Answer 29

Stage 1: very moment on leaving the plane
Weight is downwards direction, and constant
Air resistance is equal to 0N
Resultant force is equal to weight, downwards
Velocity = 0m/s
Acceleration is very large 9.8m/s2

Stage 2 (skydiver is falling)
WEight is constant
Air resistance is increasing, upwards direction
reusltant force is W - AR
Velocity is icnreasing at a fast rate initally, before still increasing but at a slower rate
Acceleration - becoming smaller but not 0 (less than 9.8m/s2 - down)

Stage 3: terminal velocity
Weight is constance
air resistance equal to weight
resultant force is 0N
velocity is constant
acceleration is 0m/s