Unit 3: Dynamics and Space Flashcards Preview

National 5: Physics > Unit 3: Dynamics and Space > Flashcards

Flashcards in Unit 3: Dynamics and Space Deck (78):
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Average Speed

Speed recorded over an extended time interval. Given symbol v bar

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Instantaneous Speed

Speed measured over an extremely short time interval

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Scalar

Quantity with magnitude only

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Vector

Quantity with magnitude and direction

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Scalar Quantities

Speed

Distance

Power

Energy

Mass

Charge

Time

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Vector Quantities

Velocity

Displacement

Acceleration

Forces

Momentum

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Distance

Scalar quantity. Total length of the path travelled in any direction

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Displacement

Length measured in a straight line from the starting point to the finishing point. Direction must also be given

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Speed

Scalar quantity. Distance travelled in unit time

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Velocity

Vector quantity. Displacement in unit time (same direction as displacement)

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Acceleration

Change in velocity per second. Vector. Given symbol a and measured in metres per second per second (ms-2)

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a = 

v-u/t

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t =

v-u/a

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v =

u + at

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u =

v - at

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V-T Graph - Positive Gradient

Straight line sloping upward to the right. Represents a constant acceleration

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V-T Graph - Zero Gradient

Horizontal Line. Represents zero acceleration

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V-T Graph - Negative Gradient

Represents a constant deceleration. Straight line sloping downwards

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V-T Graph - Area under Graph

Equal to total displacement

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V-T Graph - Average velocity

Calculated using total displacement(s) and time (t). Given symbol v bar

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Force

Vector Quantity. Given symbol F and measured in Newtons (N)

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Forces Can

Change the speed of an object

Change object's direction of travel

Change object's shape

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Friction

Force. Always opposes motion and always changes kinetic energy into heat. Present whenever two surfaces are in contact with each other and slide across each other

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Weight

Gravitational force of attraction acting on an object. Given symbol W and measured in Newtons (N)

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Balanced Forces

When the forces acting in one direction are exactly equal to forces acting in the opposite direction

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Newton's First Law

An object will remain at rest or travel with a constant velocity unless acted on by an unbalanced force

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Unbalanced Force

Force(s) acting in a particular direction are not cancelled out by force(s) acting in the opposite direction

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Newton's Second Law

When an object experiences an unbalanced force it accelerates. The acceleration is proportional to the unbalanced force acting and inversely proportional to the mass of the object

 

Fun = ma

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Newton's Third Law

For every action there is an equal but opposite reaction

If A exerts a force on B then B exerts an equal but opposite force on A

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Seatbelts and Forces

When a car stops a large frictional force is exerted on the car by the brakes providing a large backwards unbalanced force and according to Newton's Second Law a large backwards acceleration

Passenger will keep moving at a constant velocity forwards unless a large, unbalanced, backwards force acts on them

Seatbelts provide a backwards unbalanced force

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Airbags

Increase time taken for head to stop

a = v-u/t so a longer time means a lesser decelaration

Fun=ma (Newton's 2nd Law) so a smaller acceleration means a smaller force will act on the passengers head

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Terminal Velocity

When frictional force acting on an objectis equal to the weight and it falls at a constant speed

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Projectile Motion

Defined as the motion in 2 dimensions of an object under the influence of one, constant force

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Projectiles - Horizontal Motion

The motion the ball would have in the absence of gravitational attraction

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Projectiles - Horizontal Distance

Caculated using the formula: d = vh x t

where: d is the horizontal distance travelled (m)

vh is the horizontal speed of the ball (ms-1)

t is time (s)

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Projectiles - Vertical Motion

The motion the ball would have if it had no horizontal velocity - if it were just dropped from a cliff

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Projectiles - Vertical Acceleration

9.8 ms-2

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Projectiles - Vertical Speed

Calculated using equation: vv=u+at

Where: vv is the vertical speed of the ball (ms-1)

u is the initial vertical speed of the ball (ms-1)

a is the acceleration (ms-2)

t is time (s)

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Projectiles - Initial Vertical Speed

Always 0 ms-1

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Projectiles - Vertical Displacement

Found using the area under the vertical velocity-time graph

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Satellite

Projectile circling the Earth at a constant altitude

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How Satellites Work

Fall towards the Earth at the same rate as the Earth's surface is curving away from the satellite

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Satellites - Acceleration

A satellite travelling at a constant speed in a circular orbit is still being accelerated towards the Earth due to the force of gravity

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Satellites - Velocity

The direction the satellite is travelling is constantly changing so the velocity of the satellite is changing

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Satellites - Forces

The unbalanced force acting on the satellite causes a change in direction rather than speed

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Planet

Body which orbits around a central star

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Moon

Body which orbits around a planet

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Star

Large, naturally luminous gaseous body (such as the Sun) found in the centre of a solar system.

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The Sun

The star at the centre of our solar system

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Galaxy

System of billions of stars that is both spinning and moving. Our galaxy is called the Milky Way

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Andromeda

Nearest galaxy to Milky Way. It is 2.5 million light years away and is a large, spiral galaxy

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The Universe

The whole of space and contains millions of galaxies separated by empty space

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Light year

Unit of distance. (metres/m), distance light travels in one year. One light year = 9.4608x10^15 m

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Optical Telescope

A refracting telescope uses two convex lenses (mounted on either end of a light proof tube) to produce an image on the retina of an observer

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Objective lens

Produces an image at its focus partway down the tube using visible light. Larger diameter means more light can enter - so brighter image produced

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Eyepiece lens

Magnifies the image produced by the objective lens. For a large magnification the objective lens should have a long focal length and the eyepiece lens should have a short focal length

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Spectroscope

Used to split up light from a star into different wavelengths

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Continuous spectrum

The light emitted goes along the entire spectrum

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Line spectrum

Only emits certain frequencies of light

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Radio telescope

Large metal curved reflector (Large metal dish) that collects and directs the weak radio waves onto an aerial

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Gamma Ray Astronomy - Examples

The Fermi and Swift satellites use gamma Ray telescopes to investigate sources of cosmic rays to study supernova and black holes, such as the one thought to be at the centre of our galaxy

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X-Ray astronomy - Examples

Telescopes carried by satellites used for the study of black holes. Data received from outside our galaxy using x-ray telescopes indicate the presence of a massive cloud of very hot gas which provides important evidence supporting the big bang model

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Ultraviolet astronomy - Examples

Hot stars with a surface temperature greater than 10,000°C emit most of their energy as UV radiation. UV radiation detected from space has contributed to research into how stars are formed. Hubble satellite carries UV telescope

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Infrared Astronomy - Examples

Most of the universe may consist of dark matter consisting of gas and dust. Strong infrared sources are believed to be regions of space that are rich in gas and dust in which young stars are forming

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Satellite Period

The time it takes for one complete orbit of the Earth. This depends on the height of the satellite. Higher altitude means longer period

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Geostationary satellite

- Orbit 36,000km above the surface of the Earth- Orbital Period = 24 hours- Therefore satellite appears to remain above the same point on the surface of the Earth- Used for worldwide communication and provide satellite TV signals

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Launch - Mass

To achieve lift the upwards thrust must be greater than the downward forces of weight and air resistance. To reduce weight, the rockets mass must be as small as possible

 

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Launch - Speed

To escape the gravitational pull of a planet or moon a rocket must achieve 'escape velocity'. On Earth this is around 11.2 km/s

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During - Cosmic Radiation

Radiation and high energy UV, X-Ray and gamma rays will no longer be blocked by the Earth's atmosphere. These are all damaging to humans

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During - Air Pressure

As we get higher in the atmosphere air pressure falls. As pressure drops the boiling point of blood and other fluids falls

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End - Debris

Satellites left in orbit can explode leaving lots of small fragments of debris in orbit. If even a tiny piece hits a satellite or manned mission it could completely destroy it

 

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End - Re-entry

A craft returning to Earth will typically be travelling at about 11 000 ms-1 which means it has a huge amount of kinetic and gravitational potential energy to lose

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Re-entry - Mass Shedding

Since kinetic energy is proportional to mass, making the mass of a space craft as small as possible means the kinetic energy the craft needs to lose is minimal

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Re-Entry - Friction 

Good way to lose kinetic energy is maximising the amount turned into heat by friction. Unfortunately this significantly raises the temperature of the space craft

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Overcoming Heat

Covering in a thick heat shield which vaporises during re-entry (Eh=mlv)

Shuttle is positioned at a very careful angle so there is still enough kinetic energy converted into heat but astronauts are kept away from the heat 

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Benefits - Our understanding of Earth

We can use satellites to look back at Earth using visible light and other EM waves to image and provide other information about the Earth

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Polar-Orbiting Satellites

In much lower orbit around the Earth than geostationary satellites. Orbit from pole to pole around every 100 minutes and provide much more detailed images of the Earth's surface

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Benefits - Technology

Many of the technologies developed for space travel have applications in our everyfay lives. Eg.

Freeze-Drying

Solar Power

Memory Foam