Space orbital motion and waves

Gravity provides force needed to maintain  stable orbit of planets around a star and also of moons and satellites around a planet.

The moons around planets in the Solar System are natural satellites – they are made of the same material as other Solar System objects. Astronomers have sent artificial satellites (satellites that are manmade) to orbit several Solar System objects, including Jupiter, the asteroid Vesta and Mars.

Artificial satellites travel in one of two different orbits:

• polar orbits and geostationary orbits

Polar orbits take the satellites over the Earth’s poles. The satellites travel very close to the Earth (as low as 200 km above sea level), so they must travel at very high speeds of nearly 8,000 m/s.

Satellites with polar orbits are used for monitoring the weather, military applications (spying) and taking images of Earth’s surface.

When object moves in circle at a constant speed, its direction constantly changes. A change in direction causes a change in velocity because velocity is a vector quantity  it has an associated direction as well as a magnitude.change in velocity results in acceleration, so an object moving in a circle is accelerating even though its speed may be constant.

An object will only accelerate if a resultant force acts on it. For an object moving in a circle, this resultant force is the centripetal force that acts towards the middle of the circle. Gravitational attraction provides the centripetal force needed to keep planets and all types of satellite in orbit.

The gravitational attraction between two objects decreases with distance. This means that the closer the two objects are to each other, the stronger the force of gravity between them. If the force between them is greater, a greater acceleration will occur.

The greater the acceleration, the greater the change in velocity – this causes the object to move faster. This means that objects in small orbits travel faster than objects in large orbits.

The graph shows how the orbital speed of a planet changes with its distance from the Sun.

All waves can be reflected.

- Sound waves reflect off walls and buildings. This is called an echoe. 

- The angle of incidence = the angle of reflection

- The incident ray, the reflected ray and the normal line are all in the same plane. 

If asked to measure an angle, measure it from the normal to the ray. 

Refraction is the bending of light rays at a surface. Happens when entering/leaving a glass block.

When light travels from air to glass, the direction of the ray bends towards the normal. The angle of incidence is bigger than the refraction angle.

All waves are refracted at the boundary between different materials.

Refraction happens as the speed of the wave changes as it passes through different materials.The speed of light depends on the density of the material. 

Less dense material -> more dense material = slower, causing a bend towards normal.

More dense material -> less dense material = faster, causing a bend away from normal.

Lenses

Converging lens: Also known as convex lense, it is fatter in the middle.

- Used to form images in telescopes, cameras and binoculars.

- Rays of light that are parallel to the principal axis of a convex lense are refracted inwards.

Diverging lens: Also known as concave lense, is thinner in the middle. 

- The fatter the lense, the shorter the focal length.

- The distance between the centre of the lens and the focal point is the focal length.