Forces, accelerations and Newton's Laws of motion (5.6.2)

Question 1

What is Newton’s First Law applying to stationary objects?

Answer 1

If the resultant force acting on an object is zero and the object is stationary, the object remains stationary

Question 2

What is Newton’s First Law, applying to moving objects?

Answer 2

If the resultant force acting on an object is zero and the object is moving,

the object continues to move at the same speed and in the same direction.

So the object continues to move at the same velocity.

Question 3

How does Newton’s First law apply to a vehicle moving at a steady speed?

Answer 3

When a vehicle travels at a steady speed, the resistive forces (friction, air resistance) balance the driving force

so it moves at uniform velocity

Question 4

When moving at a steady speed, only when will the velocity/speed change?

Answer 4

if a resultant force is acting on the object

Question 5

What is inertia?

Answer 5

The tendency of objects to continue in their state of rest or of uniform motion

Question 6

How does mass correlate to inertia?

Answer 6

The more mass something has, the greater its inertia

so has greater tendency to continue in state of rest or of uniform motion

Question 7

What is Newton’s Second Law?

Answer 7

The acceleration of an object is proportional to the resultant force acting on the object, and inversely proportional to the mass of the object.

resultant force = mass x acceleration

Question 8

What is inertial mass?

Answer 8

a measure of how difficult it is to change the velocity of an object

inertial mass = mass

Question 9

How is inertial mass explained?

Answer 9

the ratio of force over acceleration

Question 10

What is the speed, mass and acceleration of a family car and truck?

Answer 10

Question 11

What does ∼ mean?

Answer 11

approximately (value)

Question 12

What is Newton’s Third Law?

Answer 12

Whenever two objects interact, the forces they exert on each other are equal and opposite (equilibrium)

Question 13

What are the rules of Newton’s Third Law?

Answer 13

The forces must be of the same type (i.e. push or pull), acting on different objects and if one of the forces goes away the other one does too

Question 14

Newton’s Third Law applies to (…) situations

Answer 14

equilibrium

Question 15

Explain how Newton’s Third Law applies to a person pushing a pram

Answer 15

There are contact forces between the person and the pram:

• the person pushes the pram forwards
• the pram pushes the person backwards

Forces at equilibrium

Question 16

Explain how Newton’s Third Law applies to a satellite in the Earth’s orbit

Answer 16

There are non-contact gravitational forces between Earth and the satellite:

• the Earth pulls the satellite
• the satellite pulls the Earth

Forces at equilibrium

Question 17

A car reaches a top speed which it cannot go any faster, what is the acceleration at this point?

Answer 17

0m/s² - when car has reached the top speed, there is no further change in its velocity, so there is no resultant force

Question 18

What happens to the driving and frictional forces of a car during the first two seconds of acceleration?

Answer 18

Driving force increases

Frictional force increase

Driving force > frictional force