Physics T1: Motion, Forces and Energy

D. Speed

distance travelled per unit time

F. Speed

Speed = total distance/ time taken

U. Speed

m/s

Average speed

Total distance/ Total time taken

Difference between velocity and speed

Velocity has direction as well as magnitude

D. Acceleration

Change in velocity per unit time

F. Acceleration

Change in velocity/ change in time

U. Acceleration

m/s²

D. Mass

Amount of matter in an object which is at rest relative to the observer.

U. Mass

kg

D. Weight

Gravitational force that acts on an object with mass

U. Weight

Newtons

F. Gravitational Field Strength

Weight/ mass

U. Gravitational field strength

N/kg

D. Density

Substance’s mass per unit volume

F. Density

mass/ volume

How to find density of solid objects

1) Measure mass—balance

2) For irregular shaped object find volume through displacement—submerge in a beaker of water

3) Measure initial volume of water

4) Record the difference in volume

5) Use formula to find density

How to find density of liquids

1) Place a measuring cylinder on balance + zero the balance

2) Pour some liquid into measuring cylinder.

3) Record mass and volume of liquid

4) Use formula to find density

What has a higher density, water or oil?

Water—oil with float on its surface

D. Resultant force

Single Force that has the same effect as all forces acting at a single point

D. Vector quantities

Have magnitude and direction

D. Scalar quantities

Have only magnitude and no direction

Tip-To-Tail Method

1) Draw all forces acting on object to scale

2) Draw straight line from start to finish

3) Length—Magnitude

4) Angle—Direction

E.g: “5N at angle 37° East from North

5 ways forces change motion:

• Start moving

• Stop moving

• Speed up

• Slow down

• Change direction

F. Force

Mass * Acceleration

Velocity in circular motion

Constantly changing—accelerating

Resultant force of circular motion

Perpendicular to direction of velocity

Towards centre of circle

D. Centripetal force

Force that keeps something moving in a circle

3 rules of centripetal force:

1) CP increased—speed increases

2) CP increased—radius of motion decreases

3) Mass increased—CP increases for speed and radius to stay constant

D. Solid friction

Force between 2 solid objects that are in contact, and are moving or trying to move relative to each other.

Impedes motion and results in heating.

D. Drag

Friction in a gas or a liquid

Uniform gravitational field near surface—

Without air resistance, objects would accelerate at a constant rate

Without air resistance:

Same acceleration of all objects

Same time to fall

The faster an object is moving…

The greater its air resistance

Describe objects falling through air:

1) Force of gravity much greater than resistance—accelerate

2) As speed increases—resistance increases

3) Acceleration is reduced

4) Resistance = Acceleration—resultant force is 0

5) Terminal velocity—steady, maximum speed

Terminal velocity on graph:

Apart from motion, forces can:

Stretch, compress, bend or twist

(More than one force needed)

Permanently deformed object:

Doesnt return to its original shape and length after force is removed

Load extension graph

D. Limit of proportionality

Point at which the load and extension stop being proportional

D. Spring constant

Force per unit extension

F. Spring constant

Force/ Extension

U. Spring Constant

N/cm

Apparatus when investigating link between force and extension

• Weighted stand

• Clamp

• Fixed ruler

• Spring

• Mass

Method when investigating link between force and extension

1) Measure natural length of the spring

2) Add a marker to bottom of spring

3) Add mass to spring + allow spring to come to rest

4) Record mass + New length of spring

5) Repeat this process

D. Moment

Measure of its turning effect

F. Moment

Force * perpendicular distance from pivot

U. moment

Nm

Principle of moments:

Balanced object means: total anticlockwise moments = total clockwise moments

An object is in equilibrium when

There is no resultant force on it and no resultant moment

Method: Investigating equilibrium

1) Rest a beam on a pivot until it balances

2) Hang a known mass on left side, at a fixed distance

3) Hang a second mass on right side—move mass until balanced

4) Measure distance between pivot and right mass

5) Calculate clockwise and anticlockwise moments

6) Repeat with a different mass on right

D. Center of gravity

The point through which the weight of the object acts.

Method to find center of gravity:

1) Suspend shape and plumb line from same point

2) Draw line along plumb line

3) Suspend shape from different pivot point

4) Draw another line

5) Center of gravity is where the 2 lines cross

Stable object:

1) Low center of gravity

2) wide base area

D. Momentum

Mass * velocity

What type of quantity is momentum?

Vector quantity

U. Momentum

kg m/s

Principle of conservation of momentum:

Total momentum before = total momentum after event, as long as no external forces act

D. Impulse

Size of force * length of time it acts for

F. Impulse

Force * time

Change in momentum

U. Impulse

Ns

F. Resultant force

Momentum/ change in time

7 energy stores:

1) Kinetic

2) Gravitational Potential

3) Chemical

4) Elastic

5) Nuclear

6) Electrostatic (charges)

7) Internal/ Thermal

4 ways of energy transfer:

1) Mechanically: work is done

2) Electrically: Electric current flows

3) Heating

4) Waves: e.g. light transfers energy. from sun to earth

Principle of Conservation of Energy:

Energy can be stored, transferred or dissipated—never created or destroyed.

F. Kinetic energy store

½ mass* velocity²

F. GPE energy store

Mass * gravitational field strength * change in height

Falling objects’ transfer of energy

Energy lost from gpe store = Energy gained in ke store

D. Work Done

= to energy transferred

F. Mechanical work done

Force * Distance moved

U. Work done

Joules

F. Power

Energy transferred/ time taken

U. Power

Watts or J/s

F. Efficiency

Useful energy output/total energy input * 100

TV efficiency on Sankey Diagram

F. Pressure

Force / Area

F. Pressure in liquids

Density * gravitational field strength * change in depth

U. Pressure

Pascals (Pa)

D. Non-renewable energy resource

Cannot be made at the same rate as it’s being used—will run out

2 fuels that are non-renewable

1) Fossil fuels—coal, oil, natural gas

2) Nuclear fuel—uranium, plutonium

D. Renewable energy resource

Can be made at same rate than it’s being used.

7 renewable resources

1) Solar

2) Wind

3) Water waves

4) Hydroelectricity

5) Biofuels

6) Tides

7) Geothermal

Most important use of energy resources

Generating electricity

Other uses of energy resources

• heating

• transport

Process in a fossil fuel power station

Process in Nuclear Power Stations

Environmental problems caused by burning non-renewable resources:

1) Sulfur dioxide—acid rain

2) Power stations—views spoiled

3) CO2—greenhouse effect

4) Oil Spillages—animals in sea affected

5) Nuclear waste—difficult to dispose of

6) Nuclear power stations—catastrophes

Nuclear fusion:

Nuclear reaction that releases more energy and less nuclear waste—unlimited.

Needs high temperatures

Describe how solar cells work

Generate electric currents directly from sunlight.

Pros of solar cells

1) No pollution

2) Can be used in remote areas

3) Don’t use much electricity

Cons of solar cells

1) Produce little power per unit space taken up

2) Solar power only available in daytime

3) Can’t increase power output when demand increases

D. Biofuels

Renewable energy resource created from plant products or animal dung.

Pros of biofuels:

1) Carbon neutral

2) Reliable

Cons of biofuels:

1) Lots of space needed

2) Lands of forests have been cleared out to grow biofuels.

Describe how wind turbines work

1) Sun is source of wind energy

2) Temperature of earth changes—wind made

3) Blades of turbine are rotated

4) Turn a generator

Pros of wind power

1) No pollution produced

2) No permanent damage to landscape

3) Work in large scale and small scale

Cons of Wind Power

1) Visual pollution

2) Noisy

3) Not always reliable

Describe how Geothermal Power works

Pros of Geothermal Power

1) Very reliable

2) Few environmental problems

3) Used in large scale and small scale

Cons of Geothermal Power

1) Only available in volcanic areas—rocks near surface

2) Cost of building power stations high