Forces and motion

Question 1

Length and volume

Answer 1

• Ruler is used to measure length for short distances
• Volume= LWH (length x width x height)
• To measure irregular shape volumes you have to put the object into a measuring cylinder water. It then displaces the water, making the water level rise by an amount equal tot he volume of the object.
• Micrometer can be used to measure distances that are too small to be used with a ruler

Question 2

Time

Answer 2

• An interval of time is measured by a clock or stopwatch
• The period T of a pendulum is the time it takes to complete on oscillation
• If you have multiple time values, find the mean average

Question 3

Speed

Answer 3

• Speed is the distance an object moves in a specific time frame (like one mile per hour). It is measured in m/s or km/h or mph
• It is a scalar quantity which is a quantity that only has a magnitude, therefore has to be positive

Question 4

What is a vector quantity

Answer 4

It has a direction as well as magnitude, for example velocity (which can be negative or positive)

Question 5

Speed equation

Answer 5

Speed = Distance/ time
Time= Distance/ speed
Distance= speed x time

Question 6

Acceleration equation

Answer 6

Change in velocity
______________
Time taken
-Measured in m/s²

Question 7

Distance/ time graph

Answer 7

• Gradient of graph is speed

- As speed is constant the gradient must not change (must be horizontal line)

Question 8

Speed/ time graph

Answer 8

• Gradient of line tells us acceleration
• An increase in speed is a positive acceleration and a decrease is negative
• If acceleration is not constant, line will be curved

Question 9

Forces

Answer 9

A force is a push/pull of one body on another. There are many different kinds of forces like:

• Friction, normal reaction force, gravitational force/ weight, air resistance/ drag, upthrust/ buoyancy
• A force may produce a change in size and shape of body, give an acceleration or deceleration or a change in direction depending on the direction of the force

Question 10

Friction

Answer 10

A force that opposes motion. Occurs when 2 surfaces try and slide over each other

Question 11

Normal reaction force

Answer 11

Opposing force from a surface when one object is in contact with another

Question 12

Gravitational force

Answer 12

The pull of the Earth on an object

Question 13

Air resistance/ drag

Answer 13

A force that opposes the movement of objects int he air

Question 14

Upthrust/ buoyancy

Answer 14

An upward push on an object floating in a fluid e.g a boat on water

Question 15

What are forces measured in

Answer 15

Newtons

Question 16

Relationship between force, mass, acceleration

Answer 16

F= M x A 
A= F/ M
M= F/ A

Question 17

Force is a … quantity

Answer 17

A vector quantity

Question 18

Direction of force

Answer 18

->5 + ->5 = -> 10

5-> +

Question 19

Mass and weight

Answer 19

-Mass is the property of an object that is a measure of its inertia (a resistance to acceleration), the amount of matter it contains and its influence in a gravitational field
-Weight is the force of gravity acting on an object, measured in newtons (N) and given by the formula:
W=MG (Weight= mass x gravity)

Question 20

Hooke’s law

Answer 20

• “Load force is directly proportional to extension provided that it is within its elastic limit”
• Elastic behaviour is the ability of a material to recover to its original shape after the forces causing deformation have been removed
• Once the spring has been stretched beyond its elastic limit, it will change shape permanently and will not return to its original shape (becomes plastic)

Question 21

Formula for Hooke’s law

Answer 21

Force= force constant x extension / F=kx 
Extension= current length- original length

Question 22

Key terms

Answer 22

• Limit of proportionality: point at which load and extension are no longer proportional
• Elastic limit: point at which the spring will not return to its original shape after being stretched
• Force constant (K) tells you how stiff the spring is

Question 23

Spring arrangements

Answer 23

• Springs can be connected in series (end to end) or parallel (side by side)
• Springs in parallel share the load and so extend half as much
• An arrangement of two identical springs in series will halve the force constant (half as stiff)
• Two parallel springs will double the force constant (twice as stiff)

Question 24

Centre of mass

Answer 24

• An imaginary point in a body (object) where the total mass of the body can be thought to be concentrated to make calculations easier
• For regular shaped, uniform objects, the centre of mass will be in the middle. It can be found by drawing lines of symmetry
• To find centre of mass on a flat irregular object:
• Get a flat object, get a Stan and a plumb line, punch 2 holes in your object, hang your object from the hole and attach the plumb line to the same hole, draw a vertical line where the plumb line is and repeat step four on the other hole
• Where the lines cross is the centre of mass
• Objects with a low centre of mass are stable as they are difficult to knock over

Question 25

Pressure equation

Answer 25

P= F/A