# 6.1 Rörelse i gravitationsfält

Även i detta avsnitt är Newtons Gravitationslag grunden för alla beräkningar.

Newtons Gravitationslag $F=G\dfrac{m_1m_2}{r^2} \textrm{, där } G=6.67\cdot 10^{-11} \textrm{Nm}^2 \textrm{/kg}^2$

#### Omloppshastighet (sid 215-217)

Kombinerar man Newtons Gravitationslag

The Moon’s rotation is not along the Earth’s equatorial plane

The time taken for a satellite to complete one orbit of the Earth depends on its height above the Earth - the higher the orbit of the satellite the longer it will take to orbit. The International Space Station orbits the Earth in 90 minutes at an altitude of 350km.

Geostationary satellites take 24 hours to orbit the Earth. This is the same time that Earth takes to complete one rotation and so the satellite always remains above the same point on the Earth’s surface (never write that it stays in the same place). To achieve this orbit, the satellite must be at an altitude of 36,000 km and positioned above the equator of the Earth.

Ground stations send signals to the satellite using a curved dish transmitterto transmit a strong signal. At the satellite the weakened signal is collected by a curved dish receiver. It is then amplified and finally retransmitted, at a different frequency, back to the ground using another curved dish transmitter.

With three geostationary satellites placed in orbit around the equator worldwide communication is permitted. Each satellite communicates with ground stations on different continents.

In satellite television systems the signal from the satellite is broadcast over a wide area and collected by dish aerials on people’s homes.

Here are two examples of practical applications of satellite imaging.

$F=G\dfrac{Mm}{r^2}$

$F=m\dfrac{v^2}{r}$

$v=\dfrac{2\pi r}{T}$

$G\dfrac{Mm}{r^2}=m\dfrac{v^2}{r}=m\dfrac{\left(\dfrac{2\pi r}{T}\right)^2}{r}=m\dfrac{4\pi^2 r^2}{T^2r}=m\dfrac{4\pi^2 r}{T^2}$

$G\dfrac{Mm}{r^2}=m\dfrac{4\pi^2 r}{T^2}$

$G\dfrac{M}{r^2}=\dfrac{4\pi^2 r}{T^2}$

$r^3=\dfrac{GMT^2}{4\pi^2}$

$r=\sqrt[\Large{3}]{\dfrac{GMT^2}{4\pi^2}}$

Wave Rider

#### Arthur C. Clarke, son of an English farming family, first set out the principles of the Geostationary Orbit in 1945. It took around 25 years for the first GEO spacecraft to appear.

Most often used orbits for communications satellite are geostationary, low-earth orbit, Molniya and medium-earth orbit.

A satellite in a geostationary orbit appears to be in a fixed position to an earth-based observer. A geostationary satellite revolves around the earth at a constant speed once per day over the equator. The geostationary orbit is useful for communications applications because ground based antennas, which must be directed toward the satellite, can operate effectively without the need for expensive equipment to track the satellite’s motion.As mentioned, geostationary satellites are constrained to operate above the equator. As a consequence, they are not always suitable for providing services at high latitudes: at high latitudes, a geostationary satellite will appear low on the horizon, affecting connectivity and causing multipath.

##### Lös 5.01-5.05 och i mån av tid 5.06,5.07

Även i detta avsnitt är Newtons Gravitationslag grunden för alla beräkningar.

Newtons Gravitationslag $F=G\dfrac{m_1m_2}{r^2} \textrm{, där } G=6.67\cdot 10^{-11} \textrm{Nm}^2 \textrm{/kg}^2$

#### Längs fältet (sid 218)

Kombinerar man Newtons Gravitationslag

#### På tvärs mot fältet (sid 219-221)

Lek lite med denna Java-applet.

En till.

##### Lös 5.01-5.05 och i mån av tid 5.06,5.07

Även i detta avsnitt är Newtons Gravitationslag grunden för alla beräkningar.

Newtons Gravitationslag $F=G\dfrac{m_1m_2}{r^2} \textrm{, där } G=6.67\cdot 10^{-11} \textrm{Nm}^2 \textrm{/kg}^2$

#### Korsande fält (sid 223)

Kombinerar man Newtons Gravitationslag

# 6.4 Elektronmassan

Även i detta avsnitt är Newtons Gravitationslag grunden för alla beräkningar.

Newtons Gravitationslag $F=G\dfrac{m_1m_2}{r^2} \textrm{, där } G=6.67\cdot 10^{-11} \textrm{Nm}^2 \textrm{/kg}^2$

Kombinerar man Newtons Gravitationslag

# 6.5 Orsakerna till magnetism

Även i detta avsnitt är Newtons Gravitationslag grunden för alla beräkningar.

Ampéres Hypotes Alla magnetfält beror på elektriska strömmar. Det är strömmarna inne i molekylerna som frambringar magnetism i järn och andra magnetiska ämnen.