3841679
Description
Flashcards by Nat Waterworth, updated more than 1 year ago
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Created by Nat Waterworth
about 9 years ago
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| Question | Answer |
| define newtons law of gravitiation | "gravitational force of attraction between two masses is inversely proportional to the distance between the centre of the masses squared and is proportional to the product of the two masses" |
| what is G, its value and units | universal gravitational constant 6.67x10^-11 NM^2KG^-2 |
| describe what a force - distance graph looks like | |
| whats the mass of the earth and its radius? | mass: 6.0x10^24 Kg radius:6.4x10^6 m note: if it was in Km you'd have to x1000 |
| what is a gravitational field? | a region in space in which a mass experiences a force due to gravity |
| define gravitational field strength | the gravitational field strength at a point in a gravitational field is the force acting per unit mass at a point |
| is gravitational field strength a vector or scalar? | vector |
| if a = F/m and g=F/m, what statement can be made? | the acceleration towards earth is equal to the acceleration due to gravity |
| what is a gravitational field around a spherical object called? | radial field |
| what do gravitational field lines show? | gravitational field lines show the direction of a force on a mass at a point |
| 3 features of field lines | directed towards centre of the sphere equally spaced closer together equals a stronger gravitational field strength |
| derive the formula of gravitational field strength when dependent on volume and density | g=Gm/r^2 m=pv g=Gpv/r^2 g=4GpPir^3/3r^2 g=4GpPir/3 |
| define gravitational potential and give units | the gravitational potential at a point is defined as the work done in taking unit mass from infinity to that point J/Kg |
| why is the gravitational potential around a mass always negative? | No work has to be done in taking the mass from infinity to a point closer as the gravitational force does the work. |
| define gravitational potential energy | the gravitational potential energy at a point is the work done in taking unit mass m from infinity to that point |
| formula for gravitational potential energy | -GMm/r change in Vg x m |
| 4 features of gravitational equipotentials | they are points of the same potential no work done moving along one right angles to field lines closer they are the stronger the gravitational field stength |
| in a uniform gravitational field give the formula to work out g and state whether g is constant or variable | g is constant in a uniform gravitational field g=change in Vg/ change in r |
| whats the formula to find out change in potential in a non uniform gravitational field | -Gm/r1 -(-Gm/r2 = Gm/r2 - Gm/r1 |
| derivation of time period and radius of a planet | centripetal force = gravitational force |
| why is the energy of a satellite in orbit always equal to a constant? | as the satellite orbits, as long as there are no resistive forces, the gain in kinetic energy is a loss in gravitational potential energy. also when radius increases, loss in kinetic is equal to a gain in gravitational potential energy |
| why does a satellite move around a planet at a constant speed | the centripetal force is at a right angle to the velocity of the satellite. this means there is no component of force in the direction of the velocity, therefore there is no increase or decrease in velocity as there is also no resistive forces in space. finally this means there is no work done in the direction of the velocity so the kinetic energy remains the same |
| why do astronauts appear weightless? and satellite remain in orbit? | the centripetal force of the satellite towards earths centre causes it to accelerate towards earth centre, so we can say the satellite is in free fall. the satellite is always accelerating towards earth as it has a just the right velocity at a right angle to the force that it remains in curvature of the planet, always accelerating towards earth. But also the astronaut has the same force on them. this means both the satellite and astronaut are in a state of free fall, so the astronaut appears weightless. |
| 4 features of geostationary satellites | time period 1 day remain in same position relative to earths surface so can be used to send signals from Australia to England by reflecting them off of it. equatorial - rotate above equator very far from earth |
| 4 features of polar satellites | time period of 1 hour orbit from north to south pole don't stay in same position relative to the earth used for photography of earth for for the weather and spying |
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