4 — forces

Question 1

Inertia

Answer 1

Inertia is the reluctance of an object to change its state of rest or motion due to its mass.

The greater the mass, the greater the inertia.

Question 2

Newton’s 3rd law

Answer 2

Body A exerts forcesAB on body B, body B will exert an equal and opposite forceBA on body A.

Question 3

What forces can do

Answer 3

1. Move a stationary object
2. Stop a moving object
   3.change the direction of a moving object
3. Increase speed of a moving object

Question 4

Motion of object in equilibrium

Answer 4

Forces r balanced as forces x and y are equal in magnitude and opp. In direction unless acted on by another force.

Object continues its state of motion/rest due to inertia/Newton’s First Law as no resultant force was applied to object.

Question 5

Describe action-reaction pair forces

Answer 5

X and y acting on different bodies, are equal in magnitude but opposite in direction.

Question 6

Parachute

Answer 6

1. free fall (W>Ar) -> constant acceleration (probably 10m/s^2, free fall due to gravitational acceleration)
2. increasing Ar (air resistance) opposing motion -> decreasing acceleration
3. Ar increases till = W (Weight) -> reaches terminal velocity, acceleration = 0
4. Opening of parachute causes large amount of Ar opposing motion -> speed decreases
5. Terminal velocity is reached.

Question 7

Equipment to measure force + SI of force

Answer 7

Forcemeter
SI: Newton (N)

Question 7

Newton’s First Law of Motion

Answer 7

States that every object will continue in its state of rest or uniform motion in a straight line unless a resultant force acts on it.

Question 8

Balanced forces

Answer 8

> /2 forces acting on object that produce no resultant force -> forces are balanced. Object is either at rest or moving at constant speed.

Question 9

Friction depends on

Answer 9

1. Type of surface
2. Weight pressing down

Is not dependent on the area of contact of the sliding surfaces

Question 10

Friction can be reduced with

Answer 10

1. Wheels
2. Ball bearings
3. Lubricants and polished surface
4. Air cushion

Question 11

What happens when an unbalanced force is acting on an object?

Answer 11

A change in velocity or acceleration occurs.

Question 12

Define 1N

Answer 12

The force that produces an acceleration of 1m/s² on a mass of1kg.

Question 13

Advantages and disadvantages of friction

Answer 13

A:
- we can walk without slipping
- moving objects r able to slow down when needed

D:
- cars r less efficient by up to 20%
- moving parts in engines, motors and machines suffer wear and tear

Question 14

Air resistance

Answer 14

Is a frictional force that opposes motion.

Characteristics:
It increases with the speed of the object
And the surface area of the object.

Question 15

Effect of air resistance

Answer 15

Absence of Ar: all objects fall under earth’s gravity with constant acceleration, g = 10m/s^2

Presence of Ar: falling object experiences decreasing acceleration until terminal velocity is reached, when Ar = W.

Question 16

Explain, in terms of the forces acting, why the acceleration of the tanker is not constant.

Answer 16

As the speed of the tanker increases, the water resistance acting on the tanker increases. Since the forward force of the tanker is a constant value, by Fnet = ma, the resultant force of the tanker will decrease as its speed increases.

Question 17

Force

Answer 17

A push or a pull that one object exerts on another

Question 18

Friction

Answer 18

A contact force that opposes sliding motion between 2 surfaces in contact