physical science chp 4
projectile
any object that moves through the air or space under the influence of gravity
Traveling from Earth to the Moon requires that a rocket have
any sustained speed if time isn't a factor.
You experience weightlessness
in the absence of a supporting surface. in a freely falling elevator .momentarily when you step off a chair.
Two objects move toward each other due to gravity. As the objects get closer and closer, the force between them
increases
if you are in an elevator and it accelerates upward your weight reading
is greater
If you are in an elevator and it accelerates downward your weight reading
is less
An outcome of universal gravitation is that
its discovery prompted other laws of nature. it provided prediction and discovery of planets. planets aren't cubes with sharp corners
The Moon continually falls toward Earth, but doesn't get closer because
its tangential velocity causes it to fall around as well as toward Earth.
Suppose you are in an elevator that is moving upward. As the elevator nears the floor at which you will get off, its speed slows down. During this time when the elevator is moving upward with decreasing speed, your weight will be __________.
less than your normal weight at rest
the force of gravity between two planets depend on
masses and distance apart
When you toss a projectile sideways, it curves as it falls. It will be an Earth satellite if the curve it makes
matches the curved surface of earth
if the _______ can be ignored, no horizontal force acts on the ball and its velocity is constant
retarding effect of friction
the ______ of a satellit is constant in circular orbit
speed
because of the moons _________ it falls around the earth
tangential velocity
Newton discovered
that gravity is universal
universal gravitational constant
the constant G in the equation for Newton's law of universal gravitation; measures the strength of gravity. has the same magnitude as the gravitational force between two 1-kg masses that are 1 m apart: 6.67 x 10 ^-11 N
The fastest moving planet in a solar system is the
the planet nearest the sun
After a rock that is thrown straight up reaches the top of its path and is starting to fall back down, its acceleration is
the same as it was at the top of its path.
law of universal gravitation
the scientific law that states that every object in the universe attracts every other object
Parabola
the trajectory of a projectile that accelerate only in the vertical direction while moving at a constant horizontal velocity
What happens to an object close to Earth's surface if it is given a speed exceeding 11.2 km/s?
It has escape velocity and moves away from the Earth never returning. It then enters an orbit about the Sun
The planet Jupiter is about 300 times as massive as Earth, yet on its surface you would weigh only about 3 times as much. This is because
Jupiter's radius is 10 times Earth's radius.
What connection does Earth's curvature have with the speed needed for a projectile to orbit Earth?
The speed has to be great enough that the distance the projectile falls each second matches the Earth's curvature.
When the distance between a pair of stars decreases by half, the force between them
increases by 4 times as much
for an initial speed greater than 8 km/s the satellite _______ a circular path
overshoots
The perturbations of Uranus led to what greater discovery?
pluto
the force of universal gravitation for two bodies is directly proportional to the __________ of there masses and inversely proportional to the _______ of the _____ separating them
product; square of the distances
satellite
projectile that falls around earth not into it
Mass is an unchanging property of an object that does not depend on _______
gravity
why do objects thrown in a the air not follow a straight line path
gravity
In what sense does the Moon "fall"?
It falls away from the straight line it would follow if there were no force on it.
Projectile curves as a result of these components
-constant motion horizontally -accelerated motion vertically
The Effect of Air Resistance on Projectiles
-with air resistance both range and altitude are decreased - without air resistance the speed lost going up is the same as the speed gained while coming down
If a projectile is fired straight up at a speed of 10 m/s, neglecting air resistance, the time it takes to reach the top of its path is
1 s
A gun with a muzzle velocity of 100 m/s is fired horizontally from a tower. Neglecting air resistance, how far downrange will the bullet be 1 s later?
100 m
Escape speed from Earth is
11.2 km/s
What is escape velocity from earth?
11.2 km/s
A softball player determines her pitching speed by throwing a ball horizontally from an elevation of 20 m above the ground. The ball lands 50 m downrange. What is her pitching speed?
25 m/s
at what launching angle is air resistance negligible
45
As the ball leaves the girl's hand, one second later it will have fallen
5 meters below the dashed line
An astronaut lands on a planet that has the same mass as Earth but half the diameter. How does the astronaut's weight differ from that on Earth?
Astronaut has four times as much weight as on Earth.
Two motorcycle stunt drivers, one light and the other much heavier, ride their motorcycles up and off an inclined ramp at identical speeds. They both rise in the air and land downrange. Neglecting air resistance, the one to attain the greatest height and greatest range is the
Both are the same.
When Dr. Hewitt releases the two projectiles, which one hits the ground first?
Both balls hit the ground at the same time.
equation for gravitational force
F=Gm1m2/r^2
When Dr. Hewitt releases the two objects, how can we tell whether one of the objects hits the ground first or whether they both hit at the same time?
We are able to hear the two balls fall.
A satellite near Earth makes a full circle in about 90 minutes. Much farther from Earth, say at the distance to the Moon, time for a full circle would be
about 28 days
the work on the payload (rocket) is stronger when it is
closer to earth
A rock is thrown upward at 50° with respect to the horizontal. As it rises, its vertical component of velocity
decreases
If Earth's mass somehow decreased with no change in its radius, your weight would
decreases also
When no air resistance acts on a fast-moving baseball, its acceleration is
downward
weight
objects force it exerts against a supporting floor or a weighing scale
the _____ of a satellite is not changed by gravity
speed
If you are standing on a scale in an elevator, what exactly does the scale measure?
the force you exert on the scale
Planets wobble in their orbits due to
the gravitational attraction to other planets.
Without air resistance, a projectile fired horizontally at 8 km/s from a mountain top will
trace a curve that matches Earth's curvature. accelerate downward at g as it moves horizontally. return to its starting position and repeat its falling behavior
1 N at earth's surface weighs only 1/4 as much when it is _____ the distance from earth's center
twice
the _______ component changes with time. the _________ component remains constant.
vertical velocity; horizontal
Compared to other fundamental forces, the Universal Gravitational Constant G indicates gravity to be a relatively
weak force
Inside a freely-falling elevator your
weight is zero
For very great distances, earths gravitational force approaches but never hits
zero
if an elevator breaks and is in free fall you weight reading would be
zero
Suppose you are in an elevator. As the elevator starts upward, its speed will increase. During this time when the elevator is moving upward with increasing speed, your weight will be __________.
greater than your normal weight at rest
At what part of an elliptical orbit does an Earth satellite have the greatest speed? The least speed?
greatest, when closest; least, when furthest
The planet Jupiter takes a longer time to travel around the Sun than Earth because Jupiter
has farther to go .goes slower.
Shruti Kumar projects a ball at an angle of 30∘ above the horizontal.Which component of initial velocity is larger: the vertical or the horizontal?
horizontal
Shruti Kumar projects a ball at an angle of 30∘ above the horizontal.Which of these components undergoes the least change while the ball is airborne?
horizontal
A ball is thrown horizontally from the top of a tall cliff. Three seconds later, the ball has fallen a vertical distance of
45 m
A projectile is launched straight upward at 50 m/s. Neglecting air resistance its speed upon returning to its starting point is
50 m/s
What is the force of gravity on a 500-N woman standing on Earth's surface?
500 N
a ball tossed at an angle of 30 degrees with the horizontal will go as far down as one tossed at the same speed at an angle of
60
how fast does something have to be launched to follow the curvature of earth
8 km per second
For equal launching speeds the same range is obtained from two different projection angles a pair that add up to
90 degrees
Earths _______ slows the payload down but never hits zero
gravitational pull
Phil works on the 15th floor of an office building, and his wife Jean works on the 30th floor, which is twice as high as Phil's workplace. Is the force of gravity half as much in Jean's workspace as in Phil's? Explain why or why not.
Gravitational force is measured with respect to distance from Earth's center; since the workplaces are practically the same distance from Earth's center any difference due to gravity is negligible.
Why do the two objects hit the table at the relative times that they do?
Gravity pulls the same amount on both, and they both drop the same distance.
As the rocket gets farther from earth, _________ between the rocket and earth decrease
gravitational strength
How will the ball's speed affect the time it takes to reach the can once the ball leaves the end of the table? (Does a faster ball take a longer time to hit the floor?)
Since the ball leaves the table horizontally, its speed will not affect the time it takes to reach the floor.
Why does the gravity in the Space Shuttle compare with the gravity on Earth the way it does?
The Space Shuttle and the surface of the Earth are about the same distance from the center of the Earth.
Why do the astronauts in the Space Shuttle float around?
The Space Shuttle is in free fall, so the shuttle and the astronauts inside it are continuously falling toward the Earth. They thus experience apparent weightlessness.
Which ball (if either) has the greatest speed at the moment of impact?
The ball thrown horizontally
As you found in Part A, your weight will be greater than normal when the elevator is moving upward with increasing speed. For what other motion would your weight also be greater than your normal weight?
The elevator moves downward while slowing in speed
How does the gravity in the Space Shuttle compare with the gravity on Earth's surface?
The gravity in the Space Shuttle is approximately equal to the gravity on the surface of the Earth.
If a satellite were beyond Earth's gravity, what path would it follow?
a straight line
A very massive object A and a less massive object B move toward each other under the influence of gravity. Which force, if either, is greater?
both forces on each other are the same
A hunter fires a bullet from a horizontally—held rifle while simultaneously dropping another bullet from the side of the rifle. The bullet to hit the ground first is
both hit at the same time
If the mass of one planet is somehow doubled, the force of gravity between it and a neighboring planet would
double- if one mass doubles the force between them doubles
oval paths in which planets move around the sun
ellipses
speed varies in a
elliptical orbit
Your weight is equal to mg when you are
firmly supported on a horizontal surface and in equilibrium
the greater seperation d, the weaker the ______ of attraction,
force
the greater the masses m1 an m2 the greater the _______ of attration between them
force
Consider two planets in space that gravitationally attract each other. If the masses of both planets are doubled, and the distance between them doesn't change, then the force between them is
four times as much
a satellite moving in a circular orbit is a special form of
free fall
Consider a space pod somewhere between Earth and the Moon, at just the right distance so that the gravitational attractions to Earth and the Moon are equal. Is this location nearer Earth or the Moon?
nearer the Moon
With no air resistance a projectile fired horizontally maintains its horizontal component of velocity because
no horizontal forces act on it.
If the masses of two planets doubles and the distance between them also doubles, the force between them would be
none of the above
if the masses of 2 planets are each doubled the force of gravity between them
quadruple
If the distance between two asteroids is doubled, the gravitational force they exert on each other will
reduce by one quarter
inverse square law
relates the intensity of an effect to the inverse square of the distance from the cause
A rock is thrown upward at 50° with respect to the horizontal. As it rises, its horizontal component of velocity
remains unchanged.
