Circular Motion and Gravitation Review

True or False: If the mass of the Earth were doubled and the radius of the earth were doubled, then the two changes would offset each other and the acceleration of gravity on its surface would still be approximately 10 m/s2.

false; g is approximately 10 m/s/s on earth's surface. Doubling the mass of the earth would increase g to approximately 20 m/s/s. Then doubling the distance from the surface of the earth to its center would decrease g by a factor of 4. The new acceleration of gravity value would be approximately 5 m/s/s. Clearly, these two alterations do not offset each other.

True or false: The gravitational force only acts between very, very massive objects

false; gravitational forces are universal (Newton's big idea); they act between any two objects which have mass.

True or false: The object experiences a force which has a component directed parallel to the direction of motion.

false; if the motion is in a circle at constant speed, the net force is perpendicular to the direction of motion and there is neither a component parallel nor anti-parallel to the direction of motion.)

True or false: Inertia causes objects to move in a circle.

false; it is centripetal force which causes the circular motion. Inertia (which is NOT a force) is merely the tendency of any moving object to continue in its straight-line constant speed path.

True or False: Increasing the mass of an object will increase the acceleration of gravity experienced by the object.

false; like statement A, this statement makes a claim that the acceleration of gravity depends upon the mass of the object. It does not. In the derivation of g from the Universal Gravitation equation, the mass cancels

True or false: Orbiting astronauts do not experience a force of gravity; this explains why they feel weightless.

false; orbiting astronauts must be experiencing the force of gravity. Without this force, there would be no centripetal force and no orbit.

True or false: It an object is placed two earth-radii above the surface of the earth, then the force of gravitational attraction between the object and the earth will be one-fourth the magnitude as on earth's surface.

false; placing the object at two earth-radii above earth's surface will put 3-earth radii from earth's center. This is equivalent to increasing the separation distance by a factor of 3; this decreases the force by a factor of 9.

True or False: The acceleration and the net force vector are directed perpendicular to each other.

false; the acceleration and net force are always directed in the same direction. In this case, F and a are directed inward; this happens to be perpendicular to the tangential velocity vector.

True or False: The acceleration of the object is directed tangent to the circle.

false; the acceleration is directed inwards; only the velocity is directed tangent to the circle.

True or False: The acceleration of gravity experienced by objects located near to (and far from) from the earth depends upon the mass of the Earth.

true; check out the equation again. The acceleration of gravity created by the earth depends upon the earth's mass.

True or False: The acceleration of gravity experienced by objects located near to (and far from) the earth is inversely related to the distance between the center of the object and the center of the earth.

true; check out the equation one more time. The separation distance is located in the denominator of the equation, indicating an inverse relationship.

True or false: If object A gravitationally attracts object B with a force of X Newtons, then object B will also gravitationally attract object A with the same force of X Newtons.

true; for every action there is an equal and opposite reaction. This is Newton's third law, an inescapable reality about forces.

True or False: Doubling the distance between an object and the earth's center will decrease the acceleration of gravity by a factor of four.

true; g is inversely proportional to the square of the distance; a doubling of the distance means that you must divide the force of gravity value by 4 (22) to obtain the new force of gravity value.

True or false:The gravitational force between an object and the earth is inversely related to the distance between the object's and the earth's center.

true; if the distance is increased, then the force is decreased.

True or False: If the net force acting upon the object is suddenly reduced to zero, then the object would suddenly depart from its circular path and travel tangent to the circle.

true; if the net force is 0 N, then the moving object will maintain its state of motion. At the instant that Fnet becomes 0 N, the object is moving tangent to the circle.

True or False: The acceleration of an orbiting satellite is equal to the acceleration of gravity at that particular location.

true; the acceleration of gravity is the acceleration which is caused by gravity when it is the only force. For an orbiting satellite, gravity is the only force.

True or false:The gravitational force can ALWAYS be accurately calculated by multiplying the object mass by the acceleration of gravity (m•g).

true; this is always the case. It is not true however to say that the gravitational force is equal to mass•9.8 m/s/s. The value of g varies with location and so at distances significantly further from the earth's surface, g is reduced and the gravitational force must be computed using a different value of g.

True or False: If the mass of the Earth were doubled (without an alteration in its radius), then the acceleration of gravity on its surface would be approximately 20 m/s2.

true; according to the equation, the g value is directly proportional to the mass of the earth. An increase in M results in a proportional increase in g.

True or False: There can be a force pushing outwards on the object as long as the net force in inwards.

true; an object which moves in a circle must have a net inward force. There are many instances of individual outwards forces which are exceeded by an individual inward force

G=?

6.673*10^-11

A car makes a sharp right-hand turn along a level roadway. a. gravity b. normal c. tension d. applied e. friction f. spring g. electrical h. magnetic

Friction (Once the wheels are turned, friction can push perpendicular to the wheels' direction, pushing the car towards the center of the circle.)

The moon orbits the earth. a. gravity b. normal c. tension d. applied e. friction f. spring g. electrical h. magnetic

Gravity (All masses attract with a force of gravity. In the case of the moon and the earth, gravity pulls on the moon in a direction which is roughly perpendicular to its path.)

A roller coaster car passes through a loop. Consider the car at the bottom of the loop. a. gravity b. normal c. tension d. applied e. friction f. spring g. electrical h. magnetic

Normal (There are two forces at the bottom of the loop; gravity pulls outwards from the center; but the normal force exceeds the magnitude of gravity, pushing inwards with sufficient force to supply the needed centripetal force.)

An eraser is tied to a string swung in a horizontal circle. a. gravity b. normal c. tension d. applied e. friction f. spring g. electrical h. magnetic

Tension (A string is attached to the eraser and pulls it towards the center point of the circle.)

True or false: The gravitational force acting upon an object is the same as the weight of the object.

true; weight and gravitational force are synonymous.

True or False: Because the speed is constant, the acceleration is zero.

false; acceleration occurs when there is a change in velocity. Since the direction of the velocity vector is changing, there is an acceleration - an inward acceleration.

True or False: The acceleration of gravity experienced by objects located near to (and far from) from the earth depends upon the mass of the object.

false; check out the equation - g = GMcentral/R2. The value of g does not depend upon the object's mass.

True or false: The doubling of the separation distance (measured from the center) between two objects will halve the gravitational force between the objects.

false; doubling the separation distance will make the force one-fourth the size.

True or false: The gravitational force between two objects is independent of the mass of the smaller of the two objects.

false; gravitational force is dependent upon the product of the two masses. Both masses are important in the computation.