PHYS 121 EXAM 2 QUESTIONS WITH VERIFIED
ANSWERS
What is uniform circular motion? - answers - when an object moves in a circle at
constant speed (v)
Where does instantaneous velocity point towards in uniform circular motion? - answers -
it's always tangental to the circular path
If the speed is constant in uniform circular motion, is there any acceleration? - answers -
yes, if the direction of velocity changes, "a" exists
If acceleration exists, is there a net force? - answers - yes, but in which direction
Which direction does acceleration, ergo net force, point? - answers - the direction points
inwards, towards the center of the circular path
Does the centripetal acceleration affect the magnitude of the velocity (v)? - answers -
no, it just directs it radially inward, helping to maintain a constant circular path & speed
What is the direction of the net force in uniform circular motion? - answers - fnet is
always in the same direction of "a", so the net force must be directed radially inward
Called the centripetal force (fc)
Which directions are positive and negative in he uniform circular motion model? -
answers - forces directed inwards are positive (+) and forces directed away the center
are negative (-)
Is there such thing as a centrifugal (radially outwards) force? - answers - no, what
happens is that the natural tendency of the object to move in a straight line must be
overcome
If the centripetal force vanishes, the object flies off tangent to the circle
How does a car go around a turn without slipping? What are those forces acting on the
car? - answers - when a car goes around a curve, there must be a net force towards the
center of the circle (if the road is flat, that force is supplied by static friction)
The car will skid if the frictional force is insignificant and the tendency of the car to move
more nearly in a straight line will overcome
Is the friction force on the turning tires static or kinetic? - answers - if the tires do not
slip, the friction is static
, If the tires do slip, the friction is kinetic
What are the 2 reasons why the tires slipping bad in terms of frictional forces? -
answers - 1) the kinetic frictional force is smaller than the static
2) the static frictional force can point towards the center of the circle, but the kinetic
frictional force opposes the direction to regain control of the car and continue around the
curve
(until static fraction is maintained again)
Where does acceleration point if an object is moving in a circular path, but at varying
speeds? - answers - the object must have a tangential component to its acceleration as
well as a radial one (to find the vector, or total acceleration)
How do you find the total acceleration for non-uniform circular motion? - answers - you
add the vector components:
A(total)= a(radial) + a(tangential)
What does newton's law of universal gravitation say? - answers - the origin of all earth's
gravitational forces comes from the earth's mass --> and this force keeps the moon in
orbit
The earth exerts a downward force on you, and you exert an upward force on the earth
Why do we we not feel our upward force on the earth (the reaction force)? - answers -
bc there is such a disparity in masses, the reaction force is undetectable, but for more
equal masses, it can be significant
How does gravitational force related to masses of the 2 bodies and distance between
them? - answers - the force is proportional to both masses, and the gravitational force
decreases by the inverse square of the distance between the 2 masses
What did the cavendish experiment do? - answers - the experiment was able to
reproduce the constant "g" and it proved that "g" is universal
What are the 2 approximations for the universal law of gravitation equation? - answers -
- proximity: if an object's size is <<< r, the object acts as if it's a point mass
- symmetry: a spherical object (due to its symmetry) acts as if all its mass is located at
its geometric center
How can you relate the gravitational constant to the local acceleration of the gravity? -
answers - g = [g( mass of earth)]/ (radius of the earth)^2
Is your acceleration due to gravity the same over all of earth's surface? - answers - no, it
varies over the surface due to altitude, local geology, and the shape of the earth (which
isn't quite spherical)
ANSWERS
What is uniform circular motion? - answers - when an object moves in a circle at
constant speed (v)
Where does instantaneous velocity point towards in uniform circular motion? - answers -
it's always tangental to the circular path
If the speed is constant in uniform circular motion, is there any acceleration? - answers -
yes, if the direction of velocity changes, "a" exists
If acceleration exists, is there a net force? - answers - yes, but in which direction
Which direction does acceleration, ergo net force, point? - answers - the direction points
inwards, towards the center of the circular path
Does the centripetal acceleration affect the magnitude of the velocity (v)? - answers -
no, it just directs it radially inward, helping to maintain a constant circular path & speed
What is the direction of the net force in uniform circular motion? - answers - fnet is
always in the same direction of "a", so the net force must be directed radially inward
Called the centripetal force (fc)
Which directions are positive and negative in he uniform circular motion model? -
answers - forces directed inwards are positive (+) and forces directed away the center
are negative (-)
Is there such thing as a centrifugal (radially outwards) force? - answers - no, what
happens is that the natural tendency of the object to move in a straight line must be
overcome
If the centripetal force vanishes, the object flies off tangent to the circle
How does a car go around a turn without slipping? What are those forces acting on the
car? - answers - when a car goes around a curve, there must be a net force towards the
center of the circle (if the road is flat, that force is supplied by static friction)
The car will skid if the frictional force is insignificant and the tendency of the car to move
more nearly in a straight line will overcome
Is the friction force on the turning tires static or kinetic? - answers - if the tires do not
slip, the friction is static
, If the tires do slip, the friction is kinetic
What are the 2 reasons why the tires slipping bad in terms of frictional forces? -
answers - 1) the kinetic frictional force is smaller than the static
2) the static frictional force can point towards the center of the circle, but the kinetic
frictional force opposes the direction to regain control of the car and continue around the
curve
(until static fraction is maintained again)
Where does acceleration point if an object is moving in a circular path, but at varying
speeds? - answers - the object must have a tangential component to its acceleration as
well as a radial one (to find the vector, or total acceleration)
How do you find the total acceleration for non-uniform circular motion? - answers - you
add the vector components:
A(total)= a(radial) + a(tangential)
What does newton's law of universal gravitation say? - answers - the origin of all earth's
gravitational forces comes from the earth's mass --> and this force keeps the moon in
orbit
The earth exerts a downward force on you, and you exert an upward force on the earth
Why do we we not feel our upward force on the earth (the reaction force)? - answers -
bc there is such a disparity in masses, the reaction force is undetectable, but for more
equal masses, it can be significant
How does gravitational force related to masses of the 2 bodies and distance between
them? - answers - the force is proportional to both masses, and the gravitational force
decreases by the inverse square of the distance between the 2 masses
What did the cavendish experiment do? - answers - the experiment was able to
reproduce the constant "g" and it proved that "g" is universal
What are the 2 approximations for the universal law of gravitation equation? - answers -
- proximity: if an object's size is <<< r, the object acts as if it's a point mass
- symmetry: a spherical object (due to its symmetry) acts as if all its mass is located at
its geometric center
How can you relate the gravitational constant to the local acceleration of the gravity? -
answers - g = [g( mass of earth)]/ (radius of the earth)^2
Is your acceleration due to gravity the same over all of earth's surface? - answers - no, it
varies over the surface due to altitude, local geology, and the shape of the earth (which
isn't quite spherical)
