What did Newton discover about gravity? |
1) The equation for the force of gravity 2) The law of universal gravitation 3) The Newtonian synthesis |
What is the Newtonian synthesis? |
The union of terrestrial laws and cosmic laws |
In what sense does the Moon "fall"? |
It falls away from the straight path that it would follow if there were no forces acting on it. |
State Newton's law of universal gravitation in words. Then do the same with one equation |
The force is proportional to the product of two masses and inversely proportional to the square of the distance between their center: F ~ m1m2/d^2 |
What is the magnitude of the gravitational force between two 1-kg bodies that are 1 m apart? |
6.67 x 10^-11 |
What is the magnitude of Earth's gravitational force on a 1-kg body at Earth's surface? |
10 kg |
When G was first measured by Henry Cavendish, newspapers of the time hailed his experiment as the "weighing Earth experiment." Why? |
With a known mass, a scale, and the radius of Earth, you can calculate the unknown mass of Earth if you know G. |
How does the force of gravity between two bodies change when the distance between them is doubled? |
The force decreases to 1/4 of its initial value |
How does the thickness of paint sprayed on a surface change when the sprayer is held twice as far away? |
It is 1/4 as thick |
Where do you weigh more: at the bottom of Death Valley or atop one of the peaks of the Sierra Nevada? Why? |
You weigh more in Death Valley because you are closer to the center of Earth |
Would the springs inside a bathroom scale be more compressed or less compressed if you weighed yourself in an elevator that was accelerating upward? Downward? |
More compressed while accelerating upward, but less compressed while accelerating downward |
Would the springs inside a bathroom scale be more compressed or less compressed if you weighed yourself in an elevator that was moving upward at constant velocity? Downward at constant velocity? |
There would be no more compression and no more expansion for both upward and downward motion |
When is your weight measured as mg? |
For a non-accelerating mass near the surface of Earth |
Give an example of when your weight is greater than mg. Give an example of when your weight is zero. |
Your weight is greater than mg when you are accelerating upward. Your weight is zero when you are in free fall |
Why are occupants of the International Space Station weightless ? |
They are in free fall |
Do tides depend more on the strength of gravitational pull or on the difference in strengths? Explain. |
Tides depend only on the difference |
Describe how the gravitational forces from the Sun and the Moon compare from one side of Earth to the other |
The Sun exerts stronger force on the side of Earth nearest the Sun, and the Moon exerts a stronger force on the side nearest the Moon |
Which has the higher tides: spring tides or neap tides? Why? |
Spring tides are higher, because the tides from the Moon and Sun add together |
Do tides occur in the molten interior of Earth for the same reason that tides occur in the oceans? |
yes, due to the difference in gravitational force across the core |
Why are all tides greatest at the time of a full Moon or new Moon? |
At full Moon and new Moon, the tides from the Moon and the Sun add because they are in line with Earth |
Would a torque on the Moon occur if the Moon were spherical, with both its center of mass and center of gravity in the same location? Why? |
No. The torque requires a distance between the center of mass and the center of gravity |
What is a gravitational field, and how can its strength be measured? |
It is a force on any body with mass. its strength is the force per unit mass on a test mass |
What is the magnitude of the gravitational field at Earth center? |
Zero N/kg |
For a planet of uniform density, how would the magnitude of the gravitational field halfway to the center compare with the field at the surface? |
g/2m/s^2 |
What would the magnitude of the gravitational field be anywhere inside a hollow, spherical planet? |
Zero N/kg |
Newton viewed the curving of the path of a planet as being caused by a force acting on the planet. How did Einstein view the curved path of a planet? |
Moving in curved 4-dimensional spacetime |
If Earth shrank, but there was no change in its mass, then what would happen to your weight at the surface? |
It would increase |
What happens to the strength of the gravitational field at the surface of a star that shrinks? |
It increases |
Why is a black hole invisible? |
The escape velocity of the black hole is greater than the speed of light |
What was the cause of perturbations discovered in the orbit of the planet Uranus? What later discovery did this lead to? |
Neptune caused the perturbations, and later Pluto was discovered |