Astr Week 2

What is Newton’s First Law

In the absence of force, a body at rest stays at rest, and a body in motion continues in motion

in a straight line at a constant speed

What is Newton’s Second Law

When force is applied, a body’s speed, or direction of motion, or both, will change. Force

equals mass times acceleration, F = ma, thus a = F/m

What is Newton’s Third Law

or any force, there is always an equal and opposite reaction force

Explain equations of Motion (speed, velocity, acceleration)

Speed: change in distance / change in time

Velocity: change in distance / change in time (m/s)

Acceleration: change in velocity / change in time (m/s²)

Differentiate between linear moment and angular moment

momentum is basically the force for velocity (how difficult it is to stop a moving object i.e. a truck rolling at a slow speed has massive momentum compared to a fast-flying baseball due to its larger mass)

Linear momentum: mass x velocity = mv

Angular momentum: (m x v) x orbit radius

Force: the means of changing an object’s momentum (like gravity) (momentum over time)

acceleration (change in speed over time) changes an object’s velocity and speed hence its momentum

• acceleration due to gravity at earth’s surface is 9.8m/s²

How is mass different from weight

mass: the amount of matter in an object (a measurement of inertia)

weight: the force of gravity acting on this mass

Explain this

What are the conservation laws in the universe

• conservation of momentum

• conservation of angular momentum

• conservation of energy

What is conservation of momentum

• the total momentum of interacting objects cannot change unless an external force is acting on them

• interacting objects exchange momentum through equal and opposite forces

What is conservation of angular momentum ***

the angular momentum of an object cannot change unless an external twisting force (torque) is acting on it

What are the different faces of gravity

downward toward the earth (weight of objects on the planet)

force that keeps planets in orbit (acting toward Sun pulling on the Earth )

Do objects experience a twisting force as they orbit the sun?

No, angular momentum is conserved and rotation and orbit will continue indefinitely

What determines how strong the force of gravity is? — Newton’s Universal law of gravitation

Mass of object (m₁)

Mass of object (m₂)

distance between them (r)

gravitational constant (G)

F = G ((m₁m₂)/r²)

gravitational attraction between two bodies must be proportional to their masses (the more mass an object has, the stronger the pull of its gravitational force)

What are Kepler’s 3 Laws

1. Law of orbits

   1. all planets move in elliptical orbits, with the Sun located at one of the two foci of the ellipse (distance between planet and the sun changes as it orbits, meaning the speed also changes)

2. Law of Areas

   1. planet does not travel at a constant speed —- it is faster when it is closest to the sun

3. Law of Periods

   1. The ratio of the square of a planet’s orbital period to the cube of its average distance from the sun is constant for all planets orbiting the same star

What is an ellipse

a flattened circle, meaning the distance between a planet and the Sun changes as it completes its orbit

What is a planet’s orbital period (P)

the time it takes a planet to travel once around the sun

What is Newton’s version of Kepler’s 3rd Law and what does it mean

P² = (4pi x a³)/(G(M + m))

if M»m, then we have P²=a³/M (p in years, a in AU, and M in solar masses)

a is the semimajor axis —- the average distance between the orbiting body and the thing it's orbiting

P is orbital period (seconds)

It matters because it allows astronomers to weigh the universe by calculating the exact masses of planets, stars, and even black holes just by observing their orbits

Explain Conservation of Energy

Energy cannot be created nor destroyed, but it can change form or be exchanged between objects

Explain Kinetic Energy and Gravitational Potential Energy near earth

Kinetic energy: ½ mv² ||| 1 joule = (kg)(m²s²)

Gravitational potential energy near earth: (mg)h ||| 1 Joule = (kg)(m/s²)m

• m = mass, g = acceleration due to gravity, h = height above earth’s surface

What is chemical energy

• a potential energy associated with chemical bonds

• chemical energy is released when a chemical reaction occurs

What is radiative energy and thermal energy

Light(photons) E = hc/λ

• h is Planck’s constant, c is the speed of light, λ is wavelength of light

thermal energy is the kinetic energy of many particles

What is the general formula for gravitational potential energy

What happened after Earth being formed by the collapse of a large cloud of matter

r decreased, huge amount of gravitational potential energy converted to heat in the process; total amount is earth’s gravitational binding energy

Emission, absorbtion, transmission, and reflection/scattering of light

E = mc²

^^ shows the mass and energy relationship is equal

what units do we use

kg = mass

s = time

m or km = distance

Give an example of how light travels at a finite speed

• when close to Jupiter, moons appeared to eclipse too early,

• when far from Jupiter, moons appeared to eclipse too late

• c = 300,000 km/s = λf (f = frequency)

What is Planck’s constant

6.63 × 10^-34 Joules/sec

Explain photons

light comes in little packets of energy called quanta (now called photons)

Energy per photon E = hf = hc / λ

higher frequency, shorter wavelength = more energy per photon

Is electromagnetic radiation a wave or a particle?

both

What is the inverse square law of light

intensity of a light source decreases in proportion to the square of the distance from the source (if you double the distance between a light source and subject, the light reaching the subject becomes ¼ as bright)