Forces

Question 1

What is the differecne between distance and displacement?

Answer 1

Distance
how far an object travels
scalar quanitity (no direction)
Displacement
the total straight distance from the starting to ending point
vector quantity (includes direction)

Question 2

What is the light gate equation?

Answer 2

The speed of an object when it travels through a light gate is
v = x / t
Where x is the length of the card, V is the speed and t is the time taken.

Question 3

What are the four acceleration formulae?

Answer 3

1) acceleration = change in velocity / time
2) final speed² - inital speed² = (2 x acceleration) x distance
3) final speed = inital speed + (acceleration x time)
4) Force = mass x accelleration

Question 4

What is the percentage change formula?

Answer 4

(fin - in)/in x 100

Question 5

What is newton’s first law?

Answer 5

An object will remain at stationary or moving at a constant velocity unless acted upon by a resultant force.

Question 6

What is Newton’s second law?

Answer 6

The acceleration of an object is directly proportinal to to the resultant force applied, and inversely proportional to it’s mass.
F = ma
(where f is the resultant force, m is the mass, and a is the acceleration)

Question 7

What is Newton’s Third Law?

Answer 7

Every action has an opposite and equal reaction.

Question 8

How do we calculate momentum?

(and units!)

Answer 8

p = mv
momentum (kgm/s) = mass (kg) x velocity (m/s)

Question 9

What is conservation of momentum?

Answer 9

the sum of momentum BEFORE collision = the sum of momentum AFTER collision
momentum cannot be created or destroyed.

Question 10

How do we calculate a change in momentum?

Answer 10

Δp = mv - mu
change in momentum = (final velocity x mass) - (initial velocity x mass)

Question 11

How do we calculate force from momentum?

Answer 11

Force = change in momentum / change in time

Question 12

What safety features are built into cars and what purpouse do they serve in preventing injury?

Answer 12

Air bags, crumple zones, seat belts.
- They absorb the kinetic energy transferred by collisions
- They increace the time taken for the change in momentum to happen, and therefore reduces the forces involved.

Question 13

Using ideas about momentum, describe how a rocket is launched.

Answer 13

The rocket starts at rest and has no momentum.
The rocket pushes the fuel out of the bottom of the rocket. The fuel has gained momentum in the direction of the ground (earth).
The conservation of momentum means that the rest of the rocket must gain momentum in the opposite direction. This propels (pushes) the rocket into the sky.

Question 14

What is mass?

Answer 14

The amount of matter the object contains. This is constant and remains the same regardless of gravitational field strength.

Density / Volume

Question 15

What is inertia?

Answer 15

An object’s tendency to remain stationary or in uniform motion.
The greater an object’s mass, the greater its inertia. The smaller an object’s mass the smaller it’s inertia.

Question 16

What is equation for weight

Answer 16

W = mg
Weight (N) = mass (kg) x gravitational field strength. (N/kg)

Question 17

Provide two apparaus that are used to measure WEIGHT

Answer 17

• Calibrated spring scale
• Top pan digital balance

Question 18

What is the acceleration of an object in free fall?

Answer 18

9.81 m/s² (often rounded to 10m/s²)

(accelerating at a constant rate due to gravity/weight)

Question 19

What is the centripital force?

Answer 19

When an object is in cirular motion, there is a resultant force acting in the centre of the circle, therefore the object is accelerating towards the centre.

Question 20

What is an interaction pair?

Answer 20

a set of 2 forces that are equal and opposite, acting on 2 interacting objects.

Question 21

What is centre of mass?

Answer 21

The point through which an objects weight appears to act

Question 22

Why does an object fall over?

Answer 22

Because it’s centre of mass is outside it’s perimiter

Question 23

Why shouldn’t lots of people stand on the top deck of a bus?

(2 marks)

Answer 23

More people on the top deck of buses means the centre of mass will be higher.
Therefore, a smaller tilt of the bus is required to place the bus’ centre of mass outside of its wheels, causing the bus to tip.

(2 marks)

Question 24

What is resultant force?

Answer 24

The sum of all the forces acting on an object

Question 25

What was Hooke’s Law?

Answer 25

The extention of an elastic object is directly proportional to the force applied to it

in other words, force = spring contstant x extention

(the higher the spring constant, the stiffer the spring.)

Question 26

What is the limit of proportionality?

Answer 26

When an elastic object is stretched too much, it becomes inelastically deformed and cannot return to it’s original form.

Question 27

What is the formula for the elastic potential energy stored in a spring?

Answer 27

Elastic potential energy = 1/2 x the spring constant x extention²

Question 28

What does the area under a force extention graph show?

Answer 28

The total elastic potential energy

Question 29

What is a moment?

Answer 29

A moment is the turning effect of a force around a fixed point.

Question 30

How do we calculate a moment?

Answer 30

moment = force × (perpendicular) distance (from the pivot)

Question 31

Recite the pressure formula

Answer 31

pressure (Pa) = force (n) / area