P2.2

Question 1

In an interaction pair …

Answer 1

• Each force acts on a different object
• The forces are the same size and type
• the forces act in opposite directions

Question 2

What is Newton’s third law?

Answer 2

“For every action there is an equal and opposite interaction”

Forces always come in pairs

Question 3

What is a non-contact force?

Answer 3

A force produced because an object is in a field

The objects don’t need to be in contact for the force to act

Question 4

Examples of non-contact forces

Answer 4

Electrostatics
Magnetism
Gravity

• these forces are the result of field

Question 5

What is a contact force?

Answer 5

Forces that only act when objects are in contact

Question 6

What happens to the atoms during a contact-force?

Answer 6

The bonds between atoms act like spring

You compress the bonds when you exert a force

Question 7

Example of contact forces

Answer 7

Friction
Drag
Normal contact force 
Upthrust
Tension

Question 8

What is the interaction pair for friction on a sliding box and what is the mechanism that produces it?

Answer 8

Interaction pair:
-The force of the box on the surface
-The force of the surface on the box 
Mechanism 
The atoms that make up the surface interact when rough surfaces slide over each other

Question 9

What is the interaction pair and mechanism that produces drag on a falling leaf

Answer 9

Interaction pair :
The force of the falling leaf on the air
The force of the air on the leaf
Mechanism:
The particles of the liquid or gas collide with the object and the object pushes them away

Question 10

What is the interaction pair and the mechanism that produces normal contact force acting on an elephant

Answer 10

Interaction pair:
The force of the elephant on the ground 
The force of the ground on the elephant 
Mechanism:
Solid objects deform slightly when you exert a force on them. The binds between the particles are compressed.

Question 11

What is the interaction pair and the mechanism that is produces upthrust on a floating boat

Answer 11

Interaction pair:
The force of the boat on the water
The force of the water on the boat
Mechanism:
Gravity produces pressure differences in a fluid. This pressure produces a net upwards force.

Question 12

What is the interaction pair and mechanism that produces tension in the chord of a bungee jumper

Answer 12

Interaction pair:
The force of the bungee jumper on the bungee cord
The force of the bungee cord on the bungee jumper
Mechanism:
Solid objects deform slightly when you exert a force on them. The bonds between the particles are stretched

Question 13

What does normal mean?

Answer 13

It means the force acts at right angles to the surfac

Question 14

What is a free body diagram

Answer 14

It is a diagram that shows the forces acting on a single object
You can use the diagram to predict or explain the motion of the object or do to calculations

Question 15

What is Newton’s first law?

Answer 15

“An object will continue to stay at rest or move with uniform velocity unless a force acts on it”

It takes a resultant force to change the motion (the speed or direction) or an object

Question 16

If the resultant force is 0 the speed or direction of an object won’t change
True or false

Answer 16

True

Question 17

What is inertia

Answer 17

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

Question 18

How do you calculate momentum?

Answer 18

Momentum = mass X velocity

(Kgm/s2) = (kg) X (m/s)

Question 19

What is the conservation of momentum?

Answer 19

In any collision momentum is conserved so the momentum before is equal to the momentum afterwards

Question 20

What happens in an elastic collision?

Answer 20

No energy is transferred to other stores. The energy in the kinetic stores stays the same.
In reality some energy is transferred to a thermal store by sound so the collision isn’t perfectly elastic.

Question 21

What happens when objects collide and move apart (an inelastic collision)?

Answer 21

In an inelastic collision some energy is transferred to other stores.
An example is a collision after which the velocity of combined objects is less than that of the original object.

Question 22

What can a resultant force do?

Answer 22

It can…

• change the speed of an object
• change the direction of motion of an object
• change both the speed and direction of motion of an object

Question 23

What is Newton’s second law

Answer 23

If the resultant force is not 0 the motion of an object changes.

Question 24

Calculating force

Answer 24

Force (N) = mass (Kg) x acceleration (m/s)2

Question 25

How do you explain the motion of falling objects? (Example of a skydiver)

Answer 25

• When you jump out of a plane you accelerate
• your motion changes because there is a resultant force on you
• the air exerts a force on you but the earth exerts a larger force
• as you accelerate the force of the air increases
• eventually the force of the air and earth are equal and your motion doesn’t change
  -you have reached terminal velocity
  A parachute increases the force of the air to reduce your velocity

Question 26

How do you explain the motion of rockets

Answer 26

• When a rocket takes of there is a resultant force on it that produces a large acceleration
• the burning fuel pushes exhaust gases out of the bottom of the rocket. The gases pushing in the rocket and the rocket pushing on the gases are an example of Newton’s 3rd law,
• when the force of the gases on the rocket is bigger than the force of the Earth on the rocket then the rocket will accelerate

Question 27

What is work?

Answer 27

Doing work is about using forces to transfer energy between stores.

Question 28

How do you calculate work done?

Answer 28

Work done (J) = Force (N) X distance (M)

Question 29

What is power?

Answer 29

Power tells you the rate at which energy is transferred.

Question 30

How do you calculate power?

Answer 30

Power (W) = work down (J) ➗time (s)