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PY 131 Test 2
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Gravity
Terms in this set (105)
Torque
Rotational counterpart of force. Twists or changes rotational motion of things. Force x Distance. T=0 for mechanical equilibrium. Objects rotate because of unbalanced torque.
A rotating object has:
Moment of inertia, orientation angle, rotational velocity, rotational acceleration, torques, rotational kinetic energy, angular momentum.
Rotational velocity
Rotations/sec or rotations/minute (rpm). Torque cause change in rotational velocity.
Rotational inertia
Property of an object to resist changes in its rotational state of motion. Depends on mass relatives to axis of rotation. Closer, easier to turn. Further away, harder to turn.
Centripetal force
Any force that causes an object to follow a circular path. (mv^2/r). 2x speed, 4x force. (When an automobile rounds a corner, friction between tires and road provides centripetal force that holds car in curved path.
Centrifugal force
An occupant inside a revolving or rotating system seems to experience an outward force. "Center-fleeing." Gravity is simulated by centrifugal force.
Angular momentum
Inertia of rotation of rotating objects.. Rotational inertia x rotational velocity.
Law of conservation of angular momentum
If no external net torque acts on a rotating system, the angular moment of that system remains constant.
Tangential speed
Linear sped of something moving along a circular path. Direction of motion is tangent to circumference of circle. Radial distance x rotational speed.
Tangential acceleration
When tangential speed undergoes change.
Center of mass
A point in an object that is an average of the distribution of its mass. If you draw a line straight down the center of gravity of an object of an shape and it falls inside the base of the object, it is in stable equilibrium and will balance. Objects with wide base and low center of gravity have more inertia.
Weight
m(10 m/s^2)
Universal law of gravity
2 masses are always attracted to each other. Fgravity = (G x Ma x Mb)/ r^2. G = gravitational constant.
Satellite
The pull of Earth's gravity causes satellites to continuously fall towards the Earth in such a way that it misses and ends up rotating the Earth. Communication satellites are 30,000 km above the Earth, 1 orbit = 24 hours.
Law of universal gravitation
Every body attracts every other body with a force that, for any 2 bodies, is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. Force ~ (mass1 x mass2)/distance^2
Weightlessness
Absence of support force.
Gravitational field
The influence that a massive body extends into the space around itself, producing a force on another massive body.
Projectile
Any object that moves through the air or space under the influence of gravity.
Parabola
The curved path followed by a projectile under the influence of constant gravity. At the top of the trajectory, the vertical component is 0, so the velocity of the zenith is only the horizontal component of velocity. Everywhere else along the trajectory, the magnitude of the velocity is greater.
Einstein's theory of relativity
One cannot tell the difference between acceleration and a gravitational field. Gravity bends space and time. Time moves faster in a lower gravitational field.
Black hole
Object has so much mass, gravity overwhelms it and it collapses and there is so much gravity, light cannot penetrate.
Amorphous
Noncrystalline structures are said to be amorphous, or in which atoms and molecules are distributed randomly. Creates properties such as the elasticity of rubber or tendency of glass to flow subjected to stress.
Weight density
Weight/volume.
Elasticity
Describes how much a body's shape changes when a deforming force acts on it, and how well it returns to its original shape when the force is removed. F ~ deltaX
Elastic limit
Distance beyond which permanent distortion occurs.
Coefficient of restitution
Measures elasticity and energy loss. High coefficient - bounces high, vice versa.
Tension
Something is pulled on/stretched.
Compression
Something is pushed in/squashed.
Scaling
As the size of something increases, it grows heavier much faster than the surface area increases or it grows stronger. Total surface area grows in proportion to the square of an objects linear size, whereas volume grows in proportion to the cube of the linear size.
Pressure
Ratio of force to area over which that force is distributed. P = force/area
Liquid pressure
Weight density x depth or (weight/volume) x depth.
Total pressure
Atmospheric pressure + liquid pressure. Pressure does not depend on amount/volume present, depends on depth. Liquid pressure is exerted equally in all directions.
Buoyant force
Net upward force that a fluid exerts on an immersed object. A completely immersed object always displaces a volume of liquid = to its own volume.
Archimedes principle for water
An immersed object is buoyed up by a force equal to the weight of the fluid it displaces.
Principle of immersion
A floating object displaces a weight equal to its own weight.
Pascal's principles
A change in pressure at any point in an enclosed fluid at rest is transmitted undiminished to all points of the fluid.
Surface tension
The tendency of the surface of a liquid to contract in area and thus to behave like a stretched elastic membrane.
Capillarity
The rise of a liquid in a fine, hollow tube or narrow space.
Adhesion
Attraction between water and unlike particles
Cohesion
Attraction between like substances
Thickness of atmosphere is determined by:
Kinetic energy of its molecules, which tends to spread molecules apart. Gravity tends to hold molecules together, which is why atmosphere is thicker when closer to Earth.
Atmospheric pressure
The pressure exerted against bodies immersed in the atmosphere. Results from the weight of air pressing down from above. At sea level, atmosphere pressure is 101 kPa. Density of air decreases with altitude. High pressure system = cooler temps and clear skies. Low pressure system = warm weather, rain, storms.
Barometer
Device that measure ATM.
Boyle's law
Product of pressure is a constant for a given mass of confined gas, as long as the temp remains unchanged. (p1v1 = p2v2, pv = constant).
Archimedes principle for air
An object surrounded by air is buoyed up by a force equal to the weight of the air displaced.
Bernoulli's principle
Where the speed of a fluid increases with the internal pressure in the fluid decreases.
Stagnation pressure
Increasing the pressure in a fluid by rapidly bringing it to rest. (high impulse). Greater speed + kinetic energy = lower pressure. Higher pressure = lower speed + kinetic energy.
Plasma
An electrified gas that contains ions and free electrons. Most matter in the universe is in plasma phase.
Air density
Air is more dense at low temperatures and low altitudes. Normal air pressure is about 15 PSI or 10^5 Pa.
Internal energy
The sum of all energies inside a substance. Total internal energy = # of molecules x temp.
Temperature
Internal energy of an object or # of atoms in the object.
Heat
Energy in the process of being transformed from 1 object to another.
Specific heat capacity
Measures how much heat must be added to increase the temperature of a unit mass by 1 degree celsius.
Conduction
Transfer of heat energy by molecular and electron collisions within a substance. Solids composed of atoms that have 1 or more loose outer electrons conduct heat and energy.
Convection
Transfer of heat energy in a gas or liquid by means of currents in heated fluid. The fluid moves, carrying energy with it. Occurs wherever fluids are subjected to temp differences.
Radiation
Transfer of energy by means of electromagnetic waves (radiant energy). High frequency = shorter waves. Low frequency = longer waves. Frequency ~ temperature.
Terrestrial radiation
Radiant energy emitted by earth.
Newton's law of cooling
Rate of cooling of an object is approximately proportional to the temp difference b/t the object and its surroundings.
Greenhouse effect
Warming of lower atmosphere by short-wavelength radiation from the sun. That penetrates the atmosphere, is absorbed by Earth, and is reradiated at longer wavelengths that cannot easily escape Earth's atmosphere.
Solar constant
1400 J/m^2 received from the sun each second at the top of Earth's atmosphere on an area perpendicular to the sun's rays, expressed in terms of power, 1.4 KW/m^2.
Solar power
Energy from unit time received from the sun.
A coin and a ring, each with the same mass, roll down an incline starting at the same time. Which one will reach the bottom first?
The coin.
A pizza chef tosses a spinning disk of uncooked pizza dough into the air. The disk's diameter increases during the flight, while its rotational speed
Decreases.
When doing flips off of a diving board, you'll more easily rotate when your body is
Balled up.
To turn a really tight screw, it would be easier if you were to choose a screwdriver that has a
Wide or fat handle.
While riding on a Ferris wheel at the state fair, you are seated 10 m from the axis. If you make a complete rotation every minute, what is your linear speed?
62.8 m/min.
If you were to put very large-diameter tires on your truck. Then, your speedometer will measure a speed that is
Lower than it is actually.
According to Kepler's laws, the paths of planets about the sun are
Ellipses.
According to Newton, doubling the distance between two interacting objects
Divides by 4 the gravitational force between them.
An asteroid exerts a 360-N gravitational force on a nearby spacecraft. If the spacecraft moves to a point 3 times as far from the center of the asteroid, the force will be
40 N.
An object is placed exactly halfway between the Earth and sun. The object will fall toward the
Sun.
If the moon were covered with water, tidal effects caused by the Earth would find the moon with
2 tidal bulges.
Which pulls on the oceans of the Earth with the greater force?
The sun.
Which is most responsible for the ocean tides?
The moon.
A rock is thrown upward at 50 degrees with respect to the horizontal. As it rises, its vertical component of velocity
Decreases.
A projectile is launched vertically upward at 50 m/s. If air resistance is negligible, its speed upon returning to its starting point is
50 m/s.
A bullet fired horizontally over level ground hits the ground in 0.5 second. If it had been fired with twice the speed in the same direction, it would have hit the ground in
0.5s.
What keeps satellites in orbit such as a space station from falling?
Nothing, they are falling continuously all around the Earth.
A particular Earth satellite is found to be in an elliptical orbit. The satellite travels at a faster speed when it is
Nearest the earth.
A "weightless" person in an orbiting space station is
Like the station, pulled by Earth's gravitation.
The length of a lunar month is roughly 28 days. If the moon were located farther from the Earth than it presently is, the lunar month would be
More than 28 days.
A stone archway is supported because the stones undergo
Compression.
An I-beam cuts material away from the middle of the beam and leaves material on the top and bottom. This extra material supports the beam where it experiences maximum
Both actually.
When an object is partly or wholly immersed in a liquid, it is buoyed up
By a force equal to the weight of the liquid displaced.
A rock suspended by a scale measures 5 N when held out of water and then measures 3 N when submerged in water. What is the buoyant force on this rock?
2 N.
A block of Styrofoam floats on water and the same size block of gold is submerged in the water. The buoyant force is greater
On the gold.
Dams are designed to be thicker at the bottom and thinner at the top because
water pressure is greater with increasing depth.
Some volcanic rock, called Pumice, is known to float in water. It can do this because its density is
Less than the density of water.
Buoyant forces act upward on a submerged object because
Upward pressure against the bottom is greater than downward pressure against the top of the submerged object.
Atmospheric pressure is caused by the
The weight of the atmosphere.
What is the approximate mass of a 1-square-inch column of air that extends from sea level to the top of the atmosphere?
14.7 lbs.
As a helium-filled balloon rises in the air, it becomes
Bigger.
A one-ton blimp hovers in the air. The buoyant force acting on it is
One ton.
About how high can water be theoretically lifted by a vacuum pump at sea level?
10.3 m.
If a strong wind from the west breaks a window in the north wall of a house, most of the glass will fall
Outside the house.
Two vertical tubes of equal cross-sectional areas are filled with water and mercury. If water is filled to a depth of 10.3 m and mercury to a depth of 0.76 m, both liquids have equal
Weights.
In a vacuum, an object has no
Buoyant force.
A large block of wood and a smaller block of iron on weighing scales both register the same weight - 1 ton. Taking buoyancy of air into account, which has the greater mass?
Wood.
Which is greater, an increase in temperature of 1 °C or of 1 °F?
1 degree C.
Looking at the expansion joint in the photo of Figure 15.11, would you say it was taken on a warm day or a cold day?
The photo was probably taken on a warm day. This bridge has an expansion joint to account for the expansion of the bridge due to heat. You can see how it is mildly stretched in the picture.
Would you or the gas company gain by having gas warmed before it passed through your gas meter?
The gas company gains money.
Suppose you cut a small gap in a metal ring. If you heat the ring, will the gap become wider or narrower?
Wider.
After you measure the dimensions of a plot of land with a steel tape on a hot day, you come back and re-measure on a cold day. On which day do you determine the larger area for the land?
You measure a larger area on a cold day.
What was the precise temperature at the bottom of Lake Superior at 12:01 AM on October 31, 1894?
4 degrees C.
If water had a lower specific heat, would ponds be more likely to freeze or less likely to freeze?
More likely to freeze.
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