Gravity and Motion
When is an object in orbit?
An object is in orbit when it travels around another object in space.
What would happen to an object in orbit without gravity pulling down?
It would fly off in a straight line.
What has to happen for a feather and a ball to fall at the same rate?
You have to take away air resistance.
Orbit
When an object travels around another object in space.
Free fall
When gravity is pulling an object down and no other forces are acting on it.
What is the acceleration due to Earth's gravity?
9.8m/s²
What type of force is gravity?
A non contact force of attraction between objects due to their mass
What does the law of gravitation state?
All objects attract each other through gravitational force. The strength of the force depends on the masses involved and the distance between their centers.
What direction is gravitational force directed to?
Gravitational force is directed inward.
What two factors affect the gravity between two objects?
Gravity increase as mass increases, this is directly proportionate. Gravity decreases as distance between the center of objects increases, this is indirectly proportionate.
How does mass affect gravitational force?
Greater mass results in greater gravity.
The weight of 80 kg of mass on Mercury is 296 N, almost identical to the weight of the same mass on Mars, but Mercury has much less mass than Mars! Explain how this can be. (What else could affect gravitational force?)
Mercury has a smaller radius than Mars, so the distance to the center is smaller, making the gravitational force larger.
Explain two ways to increase the gravity between two objects.
Moving the objects closer together will decrease the distance between their centers and increase the gravity between them. Increasing the mass of one or both objects will increase the gravity between them.
Why don't objects pull each other into a big pile?
The gravitational forces between these objects are too small. Other forces, such as friction, are strong enough to balance the gravitational pulls and prevent changes in motion.
Describe the law of universal gravity.
The law of universal gravitation relates gravitational force, mass, and distance. It states that all objects attract each other through gravitational force. The strength of the force depends on the masses involved and distance between them.
Why does the moon not fall to Earth?
The moon does does not fall to Earth because of its forward motion.
If Earth were replaced by an object with the same mass but much smaller in size, would the moon continue to orbit the new object, fall into it, or fly off into space? Why?
The moon would stay in orbit because the masses are the same and the distance between the centers stays the same.
Objects in space, for example the moon travel along what paths?
These objects travel along circular and elliptical paths.
Why don't satellites in orbit fall to the ground? Why don't they fly off into space?
They don't fall to the ground because they have a high forward velocity. They don't fly into space because they are in free fall to due to gravity. The two must be equal.
Gravity
A force of attraction between objects that is due to their mass.
What happens when gravity is the only force affecting the fall of a heavy and light object?
A light object and a heavy object hit the ground at the same time.
Mass
A measure of how much matter is in an object.
Describe the proportional relationships between gravitational force, mass, and distance.
Mass and gravitational force are directly proportionate because as the mass of an object increases the gravitational force also increases making mass and gravity direct proportions. Distance and gravitational force are indirectly proportionate because as the distance of an object increases, the gravitational force decreases, making distance and gravity indirect proportions.
Explain the difference between mass and weight.
Mass measure the amount of matter in an object. Weight is the force of gravity acting on that object.
How does distance affect gravitational force?
Objects closer together have a stronger gravitational attraction than objects far apart.
How do distance and mass affect gravity?
Objects with greater mass have more attraction between their centers and objects far apart have weaker attraction than objects close together.
When is an object in free fall?
Something is in free fall when gravity is pulling it down and no other forces are acting on it.
Imagine tying a string to a ball and twirling it around you. How is this similar to the moon orbiting Earth? In this example, what is providing the constantly changing, inward force?
The ball travels in an orbit around you. The tension in the string provides the force.
What two forces combine and produce orbit?
The combination of forward motion and free fall due to gravity combine cause orbit.
What causes one object to orbit another?
The free fall of an object combined with its forward velocity cause it to orbit another object.
The change in motion is due to what force?
Unbalanced forces.
The weight of an object on a planet depends not only on its mass, but also on its distance from the planet's center. Uranus has more than 14 times as much mass as Earth, yet the gravitational force is less. Explain how this could be.
Uranus has a much larger radius than Earth. The distance to the center is much greater, so the gravitational attraction is less.
What is weight and what does it depend on?
Weight is a force of gravity acting on an object and it depends on mass.
