# 14: Orbits and Escape Velocity

{'English - US': '/courses/physics/8-01-physics-i-classical-mechanics-fall-1999/video-lectures/lecture-14/lec14.srt'}

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Topics covered: Bound and unbound orbits; escape velocity. Various sources of energy, energy storage, energy conversion, and the world's energy consumption are discussed.

Instructor/speaker: Prof. Walter Lewin

Date recorded: October 13, 1999

## Video Index

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• Escape Velocity
The escape velocity is the minimum speed required to escape the gravitational pull. You can calculate it using the conservation of mechanical energy.

• Circular Orbits
The gravitational force provides the centripetal acceleration required for orbiting satellites. If you know the radius of a circular orbit of a satellite around the Earth, you can calculate the orbital speed and the orbital period. Examples are worked for both the shuttle and the moon around the Earth, and for the Earth around the sun. The orbital period is independent of the mass of the orbiting object.

• Power
Power is the rate at which a force does work on an object. Instantaneous power is the time derivative of work. Power is the dot product of the force acting on an object and the velocity of that object. Power is a scalar; it can be positive, negative, or zero. A force diagram for a bicycle rider is discussed. The required power to be delivered by the rider scales with the third power of the speed.

• Heat and Various Forms of Energy
Heat energy, calories and specific heat are discussed. Joule's experimental apparatus for converting mechanical energy into heat energy is described. Several sources of heat are mentioned (including body heat). The energy to heat up bath water is calculated. Conversion of energy from one form to another is discussed, and a student is asked to convert mechanical power to electrical power. How long will he last?

• Energy Conversion
Batteries convert chemical energy to electricity. A make-shift battery is constructed of sulfuric acid with copper and zinc electrodes to briefly light a lamp.

• Global Energy Consumption and Sources
The US has about 1/30 of the world's population but accounts for 1/5 of the global energy consumption. Harvesting solar radiation is numerically considered. Nuclear power is discussed and the public sentiment. We have an Energy Crisis! Fossil fuels could be depleted within 100 years. Nuclear fusion is being explored. The presence of radioactive uranium in Fiestaware glaze is demonstrated. (Professor Lewin has a large Fiestaware collection).