Forces and MotionChapter 2 – Gravity, Motion, and Light

Matter• Anything that has ___________ and

takes up _________.

• All matter is composed of __________

• Atoms have several subatomic particles.– _________&_________ – In the nucleus– __________ – Orbit around the nucleus

• All matter, and subsequently atoms, are subject to four forces of Nature.

Forces of Nature • – The force of attraction that is

between two bodies and is generated by their masses. – More later

• – The force arising between electrically charged particles or between charges of a magnetic field. (holds electrons to the nucleus)– More later

• force – Only important on a subatomic scale. Holds the protons to the neutrons in the nucleus.

• force – Only important at an atomic scale and is responsible for radioactive decay.

Gravity• ______________gives the universe its

structure.• It acts on _______ objects.• Every particle is drawn toward every

other particle by its pull.• – The tendency for an object

at rest to remain at rest, and a body in motion to remain in motion in a straight line at a constant speed.

• Inertia was first demonstrated by __________, but describe in to the law we know today by _________________.

Newton’s first law of motion• The ______________________.

• Objects at rest remain at rest unless a force is acted upon it. Objects in uniform motion continue moving in a straight line unless other forces act upon it.

• Newton’s first law explains how _______________________________.

• Video

Determining the rate of drop• Velocity is how fast an object is moving

in one direction.• Velocity = • V=d/t so• T = d/v• On Earth gravity causes objects to fall at

9.8 m/s2 • Notice that an objects mass has little to

do with its rate of fall in this example.• However, an objects mass has a lot to do

with how quickly an object can accelerate

Newton’s second law of motionNewton’s second law deals with a change in

direction or the acceleration of an object.• – A change in an object’s

velocity. (a deviation from uniform velocity). – Acceleration can be positive - _____________– Acceleration can be negative - _____________– A change in direction is also a change in

acceleration.

• – The amount of acceleration that a force can produce, depends on the mass of the object being accelerated.

The math behind Newton’s 2nd law• __________ = object’s mass x acceleration.

• F = ma

• Force is measured in ____________, mass in grams, and acceleration in meters/sec.

• Tomorrow, you will measure the amount of force necessary to move two objects across two different surfaces.

• Newton was able to deduce the law of gravity using the moon’s motion and applying his second law of motion.

The law of gravity• Every mass exerts a force of

attraction on every other mass. The strength of the force is directly proportional to the product of the masses divided by the square of their separation.

• OR simply : _____________________

• G is a constant = 6.67x10-11

• We will not be calculating the force of gravity between two objects

The effects of Gravity• Gravity is the force that keeps us

“______________” to the Earth.

• It also keeps the __________ orbiting around the Earth.

• The moon’s gravitational pull is what causes the ____________. –We will discuss the tides later in the

semester.

• Newton then used his first two laws to state his third law : __________-______________.

Newton’s third law of motion• When two bodies interact, they

create equal and opposite force on each other. See fig 2.8 in book.

• When I asked how would you return to the space station with only a tool box in your possession?

• We relied on Newton’s third law. The force you applied to the tool box was equal and opposite to the force that the tool box applied on you, thus it would force you to move in the opposite direction.

Pulling g’s• The term pulling g’s refers to the

gravitational attraction at a planet’s surface.• Otherwise known as _____________

gravity.• Surface gravity (g) is VERY important.– It determines: your ______________– The celestial body’s ______________– The presence &/or the components of the

___________________

• The formula for determining surface gravity is: g = GM/R2.– G = constant 6.7x10-11

– M = The mass of the attracting body– R = Radius of the attracting body

Determine your weight on the Moon• Mass of the moon = 7.3x1022

• Radius of the moon = 1.7x106

• G= 6.7x10-11

• Formula for g = GM/R2

• The g on earth = 9.8

• divide 9.8 by gmoon and that is how many times different your weight is on the moon than on earth

• Multiply your weight by that number to get your lunar weight.

Escape velocity•

• Escape velocity = √2GM/R– G = constant (6.7x10-11)– M= Mass of the body to be escaped from– R= Radius of the body to be escaped from

• The escape velocity from the moon is 2.4 km/second• The escape velocity from the Earth is 11 km/second.• Why is it easier to escape the moon than Earth?• Does escape velocity have an effect on the ability of

a planet to sustain life?