Units 3-4 Flashcards
True or False: Everything on earth is being influenced by the earth’s gravitational pull.
True
What is the symbol ‘g’ used for?
Represents the RATE of acceleration CAUSED BY GRAVITY
True or False: The standard ‘g’ is equal to something specific
TRUE
What does g equal?
22 m/h
32 ft/sec
9.8 m/sec
Why does g equal 9.8 m/sec?
It is based on the mass of the earth and the distance to earth’s center. Since most things on earth are so small compared to earth and almost equally far away (given that everything is happening on the surface of the earth) 9.8 m/sec is generally a measurement that meets most standards.
It’s mostly a standardized estimation so that you don’t have to do the math for every single object (they would all be roughly the same anyway due to the mass and distance I’ve already outlind).
How are speed and acceleration influenced if an object is falling with no friction?
Speed increases.
Acceleration is constant
True or False: Because of Newton’s 2nd law, for objects accelerating under just the influence of gravity, the acceleration, a is the gravitational acceleration, g.
TRUE
True or False: When an object falls, because the acceleration remains constant, the force the object is experiencing also remains constant.
True
F = ma
a = g
True or False: The acceleration and force of gravity are constant for any given object as it falls
True
WHY is the acceleration and force of gravity constant for any object as it falls?
Because of Newton’s 2nd law of motion.
F = ma
Gravity’s rate of accelerating an object will always (basically) be 9.8 m/sec, which is the acceleration in the equation above.
So no matter what is falling, the ‘a’ will be set to 9.8 m/sec. Given that acceleration and force are always proportional, that means that F will also be constant.
True or False: When a ball is thrown up in the air and slows down to reach the top, the rate of acceleration remains the same the whole way.
True
WHY does the rate of acceleration remain the same when a ball is thrown up in the air?
Because when you are measuring the rate of acceleration caused by the force of gravity, you will always* use 9.8 m/sec. So even though the ball is slowing DOWN, the acceleration is the same.
The pull of gravity does not depend on whether the ball is going up or down. It will always be the same.
True or False: The acceleration caused by gravity is constant, regardless of the direction of motion.
TRUE
True or False: The rate a ball slows down while traveling upward is the same rate it speeds up when coming down.
TRUE
If one ball is dropped from the same height at the same instant that another ball is thrown horizontally, which will hit the ground first?
BOTH WILL HIT AT THE SAME TIME!
Because regardless of the horizontal motion (speed of the ball), the downward acceleration is THE SAME. Gravity pulls vertically on both balls equally.
What does acceleration measure?
The way velocity CHANGES.
Why does gravity negate changes in acceleration and therefore changes in velocity?
Because the rate is ALWAYS the same (negligible differences on the surface of earth for most objects).
What is weight?
A measure of the FORCE of gravity pulling on an object.
Does weight affect how an object accelerates due to gravity?
Nope
What is the equation of weight?
Weight = mass x gravity
True or False: All objects fall at the same rate of acceleration regardless of weight (if air resistance is ignored).
True
What does air friction do to lighter objects?
It causes them to fall to earth more slowly.
True or False: Any two objects, lead weights or popcorn, when dropped in a vacuum simultaneously from the same height, will hit the ground at the same time, traveling at the same speed.
True
What type of force is holding the moon in a constant revolution at a constant speed?
Centripetal force as a result of gravity
True or False: The force of gravity diminishes with distance
True
Why does the moon stay in orbit around the earth?
Because the pull of gravity on the moon is essentially perpendicular to the moon’s velocity (ball on a string)
Why is the moon always “falling”?
Because its speed keeps it the same distance away from earth at all times. It stays in orbit, because earth’s gravity is consistently pulling perpendicularly to its velocity. Without gravity it would fly away like a ball on a string after being released.
What is the rate that gravity diminishes with distance?
1 / d^2
D is the distance between the two centers of the objects being compared.
Why does the earth “wobble” out of its rotation and revolution so much?
Because of Newton’s 3rd law. The earth’s gravity is pulling on the moon, but the moon is also pulling on the earth. Things on earth’s surface are so small that the result of gravitational pulling by earthly objects is negligible. But the MOON is large enough to exert a real change of acceleration on the earth. So it wobbles as it pulls / leans toward the moon in its rotation, whichever side the moon is on.
What did Newton learn about the relationship between mass and gravitational pulls?
The gravity between two objects depends on the mass of BOTH objects, not just one or the other
What is the equation to the law of gravity?
F = G(mM / d^2)
The strength of the force of gravity between two objects of mass M and m separated between their centers by the distance d.
True or False: The force of gravity is PROPORTIONAL to the masses of both of the objects on which it acts.
True
True or False: The force of gravity weakens as the square of the distance between the centers of two masses.
True
What is Newton’s law of gravity?
Every object in the universe attracts every other object by a long range gravitational interaction that obeys Newton’s third law. The strength of the attractive force F varies with the masses M and m, of the two objects, and the distance d between their centers.
What is the G that appears in the equation of the law of gravity?
Gravitational constant
Gravitational constant
A number relating the strength of the force to the masses being attracted and their distance apart.
It basically equals 6.67 x 10^-11
It’s so small that it only becomes valuable when the objects are planet sized or larger.
How did Newton know that every object had a gravitational force?
He didn’t. It was an untestable hypothesis at the time.
Why do we use the standard 9.8 m/sec to represent g when we know that gravity changes depending on distance?
Because the difference isn’t significant enough to measure.
When would we apply the 1 / d^2 decrease in the gravitational formula?
When we are comparing objects at distances from Earth’s surface far greater than we would encounter in normal life, such as rocket ships, satellites, and the moon (or beyond).
Are G and g the same thing?
NO
Is G truly constant?
Probably. As far as we can tell
What is the difference between G and g?
g is the acceleration of gravity, the RATE of acceleration caused by gravity
G is the measure of the FORCE of attraction.
What is the General Theory of Relativity?
Einstein’s description of gravity. This theory explains the relationship between the geometry of space and the flow of time in our universe.
Was Einstein trying to solve gravity’s question of how a law of gravity could exist in a universe that was empty?
Nope. Happy accident after he already applied it to other things.
What is the basic premise of the theory of relativity?
Large objects with gravitational pulls (like the earth) alter the space-time around them, curving it like a bowl (the universe is a geometric space). Thus, objects going near earth “fall” into orbit by falling into this “bowl” effect that planets and large objects create in the space-time around them.
Because the moon is going so fast, it stays in this circular orbit around the earth forever.
Why is it impossible for anything to escape a black hole?
Because the mass density is so great, they curve the space-time around them too steeply for anything to get out that comes near. And the area is presumably massive.
Why do heavier objects accelerate at the same time as lighter objects?
Because even though the gravity is pulling on the heavier mass more, heavier mass is harder to accelerate. They cancel out.
True or False: Everything falls the same even though gravity doesn’t pull on everything the same.
True
What is the general theory of relativity?
The theory that explains the geometry of space (3D nature) and the flow of time in the universe.
Explains that mass can WARP the geometry of space.
What is a vacuum?
Dyson (jk)
A situation where no air friction is present. There are no contact forces due to air.
What is the F in Newton’s gravitational equation?
Force of gravity
What is the d in Newton’s gravitational equation?
The separation between the two objects
True or False: When one of the objects being measured is planet size, the gravitational force on the OTHER object due to the planet is called WEIGHT.
True
True or False: The gravitational force between two people or between two objects that are smaller than planets is called weight.
False
True or False: Even though the distance between the surface of the moon and the core of the moon is LESS THAN the distance between the surface of the earth and the core of the earth, the gravitational force on objects on the moon is still less than earth’s.
True.
Basically saying that even though you are closer to the moon’s core, and therefore being pulled upon more, you still WEIGH less on the moon because the MASS of the moon is smaller.
True or False: In a vacuum, all objects accelerate the same amount, regardless of their mass.
True
True or False: Air friction is a real thing.
True
Also called air contact or air contact force
True or False: Acceleration caused by gravity DOES NOT DEPEND on the mass of the object
TRUE
Drill this into your head.
How can you prove mathematically that the mass doesn’t affect the acceleration of an object falling from gravity?
Newton’s 2nd law and his gravitational law.
F = ma
F = G(mM/d^2)
OR
ma = G(mM/d^2)
OR
a = G(M/d^2)
Which says that the acceleration of an object depends on the gravitational constant, the mass of the earth, and the distance of the object to the center of the earth (all of which are essentially null and void in the average calculation, the differences are negligible).
True or False: Einstein’s theory of relativity is mostly true but doesn’t account for everything we’ve seen in the universe.
FALSE
To date, it has not made a wrong prediction. It’s out best guess but there will still be more discoveries in the future.
True or False: Einstein’s theory of relativity contradicts Newton’s law of gravity.
True, kind of yeah
But the theory of relativity equations are looooong and difficult, and Newton’s law provides pretty accurate measurements too, so we keep using it even though it is “obsolete.”
True or False: Newton’s laws work for most but not all situations.
True
A cannonball and a marble are dropped at the same time, from the same height, with no air friction.
How do the speed and acceleration compare between the cannonball and the marble?
Speed and acceleration are both the same in this scenario.
A cannonball and a marble are dropped at the same time, from the same height, with no air friction.
How does the gravitational force compare with that of the marble?
It is LARGER on the cannonball.
A cannonball and a marble are dropped at the same time, from the same height, with no air friction.
Which is easier to accelerate?
The marble.
The cannonball requires MORE FORCE to accelerate it the same amount as the marble.
True or False: You can separate what an object is doing vertically from what it’s doing horizontally (motion).
True
True or False: A moving car can become electrified from air friction
True
True or False: The electric or electromagnetic force becomes stronger at closer distances
True
What is one key difference between the electromagnetic and gravitational forces?
The electromagnetic force can REPEL as well as attract
True or False: Charged rods made of the same material always repel each other
True
Who said that electricity was some sort of invisible fluid that began to flow when two surfaces were rubbed together?
Benjamin Franklin
What does static mean?
Unmoving
Who discovered that lightning was a manifestation of static electricity?
Benjamin Franklin
What is a Leyden jar?
A special kind of glass bottle that can hold charges like a battery.
What is the electric force law?
Pairs of objects with similar charges REPEL each other, and pairs with dissimilar charges ATTRACT each other with forces, F, that obey Newton’s third law.
The strength of F depends on the net charges, q and Q, of the objects and the distance, d, between their centers.
What is the electric force law equation?
F = k(Qq/d^2)
What does k represent in the electric force law?
Represents a number called the electric force constant.
Aka: Coulomb’s constant
8.9 x 10^9
True or False: Opposite charges attract and same charges repel.
True
What is the difference between G and k?
Other than the fact they belong to different force laws, k is relatively large (9x10^9).
Why is it important to know that k is a large force?
Because it means a tiny amount of charge will generate the same amount of force created by a huge amount of mass.
What was Franklin’s single fluid hypothesis/model?
He assumed matter had a charged fluid part embedded in an oppositely charged, less mobile part. The fluid could flow in or out of objects, leaving them positively or negatively charged.
What did J.J. Thomson do?
Discovered that electricity had mass.
He also discovered that regardless of the type of gas atoms he was tearing apart, the negative fragments (flowing toward the positive plate) always had the same charge and mass. The positive fragments however, retained the mass properties of the original gas.
His results suggested that Franklin’s “electrical fluid” was a stream of particles.
What word did “electrons” replace?
Corpuscles
What happened to the atoms of gas in the tube during Thomson’s experiments?
They were being broken into charged fragments.
What is an electron?
The negative charge-carrying particle in an atom
What did Robert Millikan do?
Developed a way to measure the charge of individual particles.
What is a Coulomb?
The unit of measure for charge
What is the amount of electric charge possessed by a single electron or proton?
1.6 x 10^-19 coulombs
True or False: Electrons are all different from each other
FALSE
True or False: Protons are all identical to each other
True
True or False: Protons carry the same amount of charge as an electron, but with the opposite sign
True
What comprises the bulk of the mass of an atom?
Protons and neutrons
True or False: Only electrons migrate to a rubbed fur or rod, never protons
False
It is rare, but protons and neutrons CAN migrate.
Why does an object become negatively charged?
Because the electrons have MOVED TO IT
Why does an object become positively charged?
Because the electrons have moved FROM IT
Which has a smaller mass, electrons or protons?
Electrons
What is the mass ratio between electrons and protons
1/1836
Do the laws of motion apply to electricity?
Yes
Which law of motion describes the attraction between the excess electrons on the bottom of thunderclouds to the excess of protons on the ground?
Third law.
The forces on each (from the other) are the same but oppositely directed.
Which of Newton’s laws explains why electrons accelerate more than protons and will therefore be the ones to break free and move?
The 2nd law
Because electrons have less mass.
What causes visible lightning?
Electrons building up on the bottom of thunderclouds being attracted to the excess of protons on the ground.
The 2nd law of motion explains why these electrons move.
What does the electrical model of matter tell us about the understanding of basic electricity?
(7 things)
- All matter contains two kinds of electrically charged particles: protons and electrons.
- Electrons have little mass so they transfer from one object to another easily.
- Protons are held rigidly in place in solid materials.
- Objects that have equal numbers of protons and electrons are electrically neutral
- Objects with more electrons than protons are negatively charged.
- Objects with fewer electrons than protons are positively charged.
- The amount of “extra” charge of either kind is called the charge of the object.
True or False: Electrons move through all materials with equal ease
False
Insulators
Materials that do not permit electrons to move freely on or within them, such as rubber.
Conductor
A material that allows electrons to flow freely onto its surface or through its interior.
Electric Current
Electric charges flowing through a conductor.
Flowing THROUGH (insulators do not allow electrons to flow through them)
Direct current
A steady flow of electrons in ONE direction, typically through a wire
True or False: Batteries produce a direct current
True
What condition must be met for an electron current to flow?
There must be a place to which the electrons can flow.
Alternating current
A current of electrons that changes direction of flow
What are lodestones?
Possibly chunks of iron ore that were struck by lightning.
They had powerful magnetic properties.
Steel needles stroked with lodestones would also become “magnetic”
True or False: A magnetic compass will always point to true north
False
Why don’t compasses point exactly North?
Because earth itself is a giant magnet, and the magnetic north pole is different from the true geographic north pole.
What makes magnets different than charged rods?
Magnets retain their attractive powers when they are handled.
Ferromagnetic
Metal alloys that are attracted to magnets
OR
Are capable of being transformed into permanent magnets
Examples of ferromagnetic material
Nickel and iron
Who proposed that earth was a giant magnet?
William Gilbert
True or False: Earth’s North pole attracts the south poles of magnets
FALSE
Earth’s north pole is actually a MAGNETIC south, and therefore attracts north poles of magnets
True or False: When you cut a magnet in half, you can keep the positive and negative sides separate.
False.
If you cut a magnet in half, the new halves will automatically become new magnets with north and south charged poles.
True or False: Either end of a magnet will attract unmagnetized ferromagnetic material.
True
True or False: Magnetism arises when electric charges move as currents
True
What is another name for the electric interaction?
The electromagnetic interaction
What is a magnetic field?
The space around electric currents in which the magnetic force is felt.
Almost like it’s range of influence.
True or False: Atoms are small magnets
True
True or False: Atoms in materials are oriented in organized patterns
FALSE
Only in ferromagnetic materials
What are domains?
A small section in a magnet where the magnetic force from all the atoms add together.
Atoms aligning with neighboring atoms in small sections. It is a NET magnetic field
What determines whether something will be a permanent magnet?
If the domains remain aligned after the external field is gone. This depends on the type of metal and the fraction of the domains that are aligned.
True or False: Permanent magnets lose their strength over time
True
Why do permanent magnets lose strength?
Because the domain alignments eventually break down.
Heat also causes domains to lose alignment
Curie Temperature
When temperatures in a metal are larger than a certain value, any magnetism it may have had will be lost.
I.E. Any magnet heated above this temperature lose their magnetism until the temperature cools, then they become magnets again.
How does the Curie temperature affect Earth?
The interior of earth is hotter than the curie temperature so it is not a permanent magnet.
Field lines
Lines coming from the object representing the strength of the force. The denser the lines, the stronger the force
How do you find field lines?
You can sprinkle iron filings on a stiff sheet of paper held near a magnet
Contact force
The force arising between objects when they touch.
They are a REPULSION caused by the electromagnetic interaction. Like pushing two positive sides of a magnet together.
Except we can’t comprehend this is happening. We THINK objects are touching, but actually, atoms from different objects don’t touch.
What are the most common manifestations of the electromagnetic interaction in our lives?
Contact and frictional forces
What is Faraday’s law?
Electromagnetic induction.
A changing magnetic field produces an electric field.
Discrete
Separate or individually distinct
Electromagnetic interaction
The interaction of moving and stationary charges to describe electric and magnetic forces
What is another term for contact force?
Normal force
Semiconductor
Something in between an insulator and a conductor
Who came up with the terms positive and negative charges?
Benjamin Franklin
What are the two differences between the law of gravity and the law of electromagnetic interaction?
- EMG is much bigger/stronger
- EMG is repulsive as well as attractive
True or False: Contact force is an electrical force
True
True or False: The contact force is always repulsive
False, although attractive force is limited
Plastic wrap sticking to itself is also contact force (dum)
Why do electrons have charge at all?
To prevent atoms from passing through each other. The force repels other atoms.
Which are weaker, electric or magnetic forces?
Magnetic
How do magnetic forces originate?
Either from permanent magnets, or from currents (moving charges)
Which moving charges create the magnetic field?
Electrons orbiting protons
True or False: Most of the time, domains are random in orientation
True
