Chapter 18
A car approaches you at 50 km/h. A fly inside the car is flying toward the back of the car at 7 km/h. From your point of view by the side of the road, the fly is moving at ______________km/h.
43
Suppose that you observe gravitational lensing as a distant object passes behind a nearer object. As the light from the more distant object bends around the nearer one, how will the brightness of the more distant object change?
It will get brighter because light rays will converge.
What will happen to the light as it passes far from the pit?
It will travel a straight-line path.
Suppose you add another bowling ball to the pit, and then roll some more golf balls and grains of sand on the rubber sheet. What statements would now be true?
The golf balls would "feel" the pit at a greater distance, the pit gets deeper and wider, the golf balls would be traveling at a greater speed upon collision with the bowling balls, and the grains of sand would behave just like the golf balls.
What happens to the depth and width of the pit as the golf balls fall into the center near the bowling ball? (Imagine putting lots of golf balls in.)
The pit gets deeper and wider.
Describe the path of the golf balls when they come just inside the edge of the dip created by a bowling ball placed in the center of the rubber sheet.
They would follow a curved path.
Imagine a big rubber sheet. It is very stiff and not easily stretched, but it does have some "give" to it. At the moment, it is perfectly flat. Imagine rolling some golf balls across it. Describe the path of the golf balls across the sheet.
They would follow a straight-line path
Astronauts in the International Space Station
are in free fall.
Some black holes are rapidly flickering X-ray sources. That observation indicates that
black holes are (at least sometimes) surrounded by hot gas.
Einstein's formulation of gravity explained:
both is approximately equal to Newton's universal law of gravitation for small gravitational fields and explained why Newton's universal law of gravitation describes the motions of masses.
A car approaches you at 50 km/h. The driver turns on the headlights. From your point of view, the light from the headlights is moving at
c
Look at Diagram: HW: 1, 5, 11, 12, 13
done
Relative motion between two objects is apparent
even at everyday speeds, such as 10 km/h.
If a spaceship approaches you at 0.5c, and a light on the spaceship is turned on pointing in your direction, how fast will the light be traveling when it reaches you?
exactly c
If a neutron star is more than three times as massive as the Sun, it collapses because
gravity overpowers the force of neutron degeneracy.
If a neutron star is more than ~2.5 times as massive as the Sun, it collapses because
gravity overpowers the force of neutron degeneracy.
As the mass of a black hole increases, its Schwarzschild radius
increases proportionately.
Imagine two protons traveling past each other at a distance d, with relative speed 0.9c. Compared with two stationary protons a distance d apart, the gravitational force between those two protons when at their closest will be
larger because the moving proton acts as though it has more mass.
Imagine you are on a spaceship. A second spaceship rockets past yours at 0.5 cc. You start a stopwatch and stop it 10 seconds later. For an astronaut in the other spaceship, the number of seconds that have ticked by during the 10 seconds on your watch is
less than 10 seconds.
If two spaceships approach each other, each traveling at 0.5c relative to an outside observer, spaceship 1 will measure spaceship 2 to be traveling
more slowly than c.
The International Space Station flies overhead. Using a telescope, you take a picture and measure its length to be _______than its length as it would be measured if it were sitting on the ground.
slightly less
