Topic 2 + 3 - Forces

Question 1

Newton’s first law (3)

Answer 1

If zero resultant force acts on stationary object, object doesn’t move
If zero resultant force acts on moving object, it continues moving at same velocity
If non-zero resultant force acts on object, object accelerates in direction of force

Question 2

Newtons 2nd law (equation)

Answer 2

F=ma
F= resultant force (N)
M= mass (kg)
A= acceleration (m/s²)

Question 3

Newton’s second law

Answer 3

Acceleration is directly proportional to resultant force
Acceleration is inversely proportional to mass

Question 4

Newtons 3rd law

Answer 4

Two interacting object exert equal and opposite forces on each other

Question 5

What is weight? (+equation)

Answer 5

Force that acts on an object due to gravity
W=mg

Question 6

How to measure weight?

Answer 6

With calibrated spring-balancer (newtonmetre)

Question 7

What is the centre of mass?

Answer 7

The point at which an objects weight appears to act

Question 8

What does object weight depend on?

Answer 8

Strength of gravitational field at object location

Question 9

True or false: object mass has same value anywhere in the universe

Answer 9

True

Question 10

What is inertial mass?

Answer 10

Measure of how hard it is to change an object’s velocity. It’s the ratio of force over acceleration

Question 11

True or false: the bigger the inertial mass, the harder it is to increase velocity

Answer 11

True

Question 12

What happens to an object in circular motion?

Answer 12

It’s always changing direction, so object has changing velocity
Changing velocity means object is accelerating, so there’s a resultant force on it

Question 13

What is the centripetal force?

Answer 13

It always acts towards the centre of the circle.

Question 14

What does mass do to momentum?

Answer 14

The greater the mass the greater the momentum.

Question 15

What does velocity do to momentum?

Answer 15

The greater an objects velocity, the greater its momentum

Question 16

Momentum (equation)

Answer 16

P=mv
P= momentum (kg m/s)
M= mass (kg)
V= velocity (m/s)

Question 17

What is conversion of momentum?

Answer 17

In a closed system, total momentum before an event equals total momentum after an event

Question 18

Typical human reaction time

Answer 18

0.2-0.9 s

Question 19

Factors affecting reaction times (3)

Answer 19

Tiredness, drugs/alcohol, distractions

Question 20

Steps to ruler drop test:

Answer 20

1. Get someone to hold ruler so zero is between your thumb and forefinger
2. Ruler dropped without warning. Catch it as quickly as possible
3. Use distance ruler fell to calculate reaction time
4. The longer the distance the longer the reaction time

Question 21

Stopping distance (equation)

Answer 21

Stopping distance = thinking distance + braking distance

Question 22

Factors that increase thinking distance (2)

Answer 22

Faster vehicle speed, long driver reaction times

Question 23

Factors that increase braking distance (4)

Answer 23

Faster vehicle speed, heavier vehicle, poor/wet/icy road surface, damaged or worn brakes/tyres

Question 24

What happens to thinking and braking distance if speed doubles

Answer 24

It quadruples

Question 25

Work done

Answer 25

1/2 x m x v² = F x d

For car to stop, work done by brakes equals energy in cars kinetic energy store

Question 26

True or false: the faster a vehicle is going, the greater the braking force needed to make it stop in a certain distance.

Answer 26

True

Question 27

What does a larger braking force mean?

Answer 27

Larger deceleration

Question 28

What can very large deceleration cause? (2)

Answer 28

Brakes to overheat, vehicle to skid