Chapter 4: Motion Energy and Gravity

• as objects fall, they accelerate
• the higher you drop a ball, the greater its velocity will be at impact
• the acceleration due to gravity is 9.81 m/s²

Galileo demonstrated that g is the same for all objects, regardless of their mass. This was confirmed by the Apollo astronauts on the moon, where there is no air resistance.

• Force: causes a change in momentum, producing acceleration
• Momentum: mass ⋅ velocity
• Acceleration: change in velocity
• Speed: distance ÷ time
• Velocity: speed with direction

• quantity of matter
• does not change

• a measurement of the force which acts upon an object
• force acting on mass
• can change
• when in "free fall," you are weightless

• 1) An object at rest will remain at rest unless acted on by an unbalanced force. Same goes for when it is in motion.
• 2) Acceleration is produced when a force acts on a mass. The greater the mass, the greater the amount of force needed. F= ma
• 3) For every action there is an equal and opposite re-action

Perhaps the greatest genius of all time. Invented the reflecting telescope. Invented calculus. Connected gravity and planetary forces.

the speed necessary for an object to completely escape the gravity of a large body such as a moon, planet or star

• b/w every two objects there is an attractive force, the magnitude of which is directly proportional to the mass of each object and inversely proportional to the square of the distance b/w the centers of the objects.

Extending Kepler's first law, Newton found that ellipses weren't the only orbital paths.

• ellipse (bound)
• parabola (unbound)
• hyperbola (unbound)

• orbital period of two objects: P is in seconds
• distance between them: a is in meters
• sum of the masses of both objects: (m1 +m2)
• G = 6.67 x 10-11m³/(kg s²)

• the momentum involved in spinning/circling 
• mass x velocity x radius

anything that can cause a change in an objects angular momentum (twisting force)

• in the absence of a net torque, the total angular momentum of a system remains constant
• ex. skater w arms out then bringing them in

orbital energy = kinetic energy + gravitational potential energy

• orbits can't change spontaneously
• an object can't crash into a planet unless its orbit takes it there
• an orbit can only change if it gains/loses energy from another object, such as a gravitational encounter

The moon's gravity stretches Earth along the Earth-Moon line, so that it buldges both toward and away from the Moon.

• gravitational attraction to the sun is greater but tides are caused by the difference between the strength of the gravitational attraction across Earth's diameter.
• the moon is much more closer than the sun, which therefore means the difference is greater for gravitational force due to the moon.

• high tides: equator, outward forces
• low tides: poles, inward forces

material such as rocks, water, air

• what makes matter move
• measured in joules
• can change from one form to another

• energy of motion/ moving energy
• amount of kinetic energy of a moving object: 1/2 mv²
• if mass is in kg and velocity is in m/s then energy is in joules
• Ek

• stored energy, mass energy
• Ep
• E = mc² 
• c = 3 x 10⁸ m/s is the speed of light. m is in kg, E is in joules

energy transported by light

• temperature: the average Ek of the particles within a substance. it's dominated by the velocities of the particles.
• heat: (thermal energy) is the total Ek

• water boils: 373.15 K, 100°C, 212°F 
• water freezes: 273.15 K, 0°C, 32°F
• absolute zero: 0 K, -273.15°C, -459.67°F

• the energy an object stores due to its ability to fall
• depends on: the objects mass, the strength of gravity, the distance which it falls (m,g,d)

• in space, an object or gas cloud has more gravitational energy when it is spread out than when it contracts. 
• a contracting cloud converts gravitational Ep to thermal energy ∴ it heats up

• energy cannot be created or destroyed
• it changes its form or is exchanged between objects
• this is a fundamental law to science

• proton/neutron -> nucleus -> electron
• electrons don't orbit the nucleus. they are "smeared out" in a cloud which gives the atom its size
• nucleus is the smallest part of the atom but it contains most of the mass
• atomic number = number of protons and electrons (in a neutral atom)
• atomic mass = sum of protons and neutrons

• same number of protons, different number of neutrons
• mass will be different

an atom or molecule with a net electric charge due to the loss or gain of one or more electrons

a group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction

• Solid: atoms/molecules are held tightly in place
• Liquid: atoms/molecules remain together but move relatively freely
• Gas: atoms/molecules move essentially unconstrained
• Plasma: free electrons move among positively charged ions

temp increases, bonds are loosened

• they can gain or lose energy while orbiting the nucleus
• atom is in ground state when the electrons have the lowest energy possible
• atom is in an excited state when the electrons have more energy than ground state
• if the electrons gain enough energy to escape the nucleus, the atom is ionized

• only certain energy values are allowed
• electrons may only gain or lose certain specific amounts of energy
• each element has its own distinctive set or pattern of energy levels