Unit 3: Dynamics and Space Flashcards
Average Speed
Speed recorded over an extended time interval. Given symbol v bar
Instantaneous Speed
Speed measured over an extremely short time interval
Scalar
Quantity with magnitude only
Vector
Quantity with magnitude and direction
Scalar Quantities
Speed
Distance
Power
Energy
Mass
Charge
Time
Vector Quantities
Velocity
Displacement
Acceleration
Forces
Momentum
Distance
Scalar quantity. Total length of the path travelled in any direction
Displacement
Length measured in a straight line from the starting point to the finishing point. Direction must also be given
Speed
Scalar quantity. Distance travelled in unit time
Velocity
Vector quantity. Displacement in unit time (same direction as displacement)
Acceleration
Change in velocity per second. Vector. Given symbol a and measured in metres per second per second (ms<strong>-2</strong>)
a =
v-u/t
t =
v-u/a
v =
u + at
u =
v - at
V-T Graph - Positive Gradient
Straight line sloping upward to the right. Represents a constant acceleration
V-T Graph - Zero Gradient
Horizontal Line. Represents zero acceleration
V-T Graph - Negative Gradient
Represents a constant deceleration. Straight line sloping downwards
V-T Graph - Area under Graph
Equal to total displacement
V-T Graph - Average velocity
Calculated using total displacement(s) and time (t). Given symbol v bar
Force
Vector Quantity. Given symbol F and measured in Newtons (N)
Forces Can
Change the speed of an object
Change object’s direction of travel
Change object’s shape
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
Weight
Gravitational force of attraction acting on an object. Given symbol W and measured in Newtons (N)
Balanced Forces
When the forces acting in one direction are exactly equal to forces acting in the opposite direction
Newton’s First Law
An object will remain at rest or travel with a constant velocity unless acted on by an unbalanced force
Unbalanced Force
Force(s) acting in a particular direction are not cancelled out by force(s) acting in the opposite direction
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
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
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
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
Terminal Velocity
When frictional force acting on an objectis equal to the weight and it falls at a constant speed
Projectile Motion
Defined as the motion in 2 dimensions of an object under the influence of one, constant force
Projectiles - Horizontal Motion
The motion the ball would have in the absence of gravitational attraction
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)
Projectiles - Vertical Motion
The motion the ball would have if it had no horizontal velocity - if it were just dropped from a cliff
Projectiles - Vertical Acceleration
9.8 ms-2
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)
Projectiles - Initial Vertical Speed
Always 0 ms-1
Projectiles - Vertical Displacement
Found using the area under the vertical velocity-time graph
Satellite
Projectile circling the Earth at a constant altitude
How Satellites Work
Fall towards the Earth at the same rate as the Earth’s surface is curving away from the satellite
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
Satellites - Velocity
The direction the satellite is travelling is constantly changing so the velocity of the satellite is changing
Satellites - Forces
The unbalanced force acting on the satellite causes a change in direction rather than speed
Planet
Body which orbits around a central star
Moon
Body which orbits around a planet
Star
Large, naturally luminous gaseous body (such as the Sun) found in the centre of a solar system.
The Sun
The star at the centre of our solar system
Galaxy
System of billions of stars that is both spinning and moving. Our galaxy is called the Milky Way
Andromeda
Nearest galaxy to Milky Way. It is 2.5 million light years away and is a large, spiral galaxy
The Universe
The whole of space and contains millions of galaxies separated by empty space
Light year
Unit of distance. (metres/m), distance light travels in one year. One light year = 9.4608x10^15 m
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
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
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
Spectroscope
Used to split up light from a star into different wavelengths
Continuous spectrum
The light emitted goes along the entire spectrum
Line spectrum
Only emits certain frequencies of light
Radio telescope
Large metal curved reflector (Large metal dish) that collects and directs the weak radio waves onto an aerial
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
Benefits - Technology
Many of the technologies developed for space travel have applications in our everyfay lives. Eg.
Freeze-Drying
Solar Power
Memory Foam
