Physics Chapter 8
The frictional quantity that is characteristic of two surfaces in contact is the ________________________ ____ ______________.
Coefficient of friction
The magnitude of the vertical component of gravity for an object resting on a flat surface is __________ ____ the normal force in magnitude.
Equal to
A free-body diagram contains more than one system.
False
A heavier box experiences the same frictional force as a lighter box
False
A moving object experiences more friction than a stationary object.
False
Area of contact does not affect friction.
False
Assuming that a string is ideal _always_ adds much error into your calculations.
False
For an object resting on an incline, the normal force is equal in magnitude to the x-component of the weight of the object.
False
Gravity does _not_ affect an astronaut performing experiments at the International Space Station,
False
The coefficient of friction is a vector quantity.
False
The equation for kinetic friction is a vector equation.
False
The magnitude of the tension in an ideal string changes when going over an ideal pulley.
False
The smoother a surface is, the more friction it can exert.
False
The values of static friction are constant for any given material.
False
Weight does _not_ affect friction.
False
On a level surface, the normal force and the force of gravity is acting on an object are vectors.
False (Their magnitudes are equal)
In an accelerated reference frame, apparent weight is equal to actual weight.
False (i.e. going up/down in an elevator)
Identify one of the forces that act on a locomotive that starts from rest to climb a hill.
Fw, Fn, fs, &c.
When is apparent weight _not_ equal to actual weight?
In an accelerated reference frame
Describe the shape of a Jersey barrier.
It's a low wedge-shaped wall used to divide opposing lanes of highway. It has 2 sections: a steep upper section & a less steep lower section.
The type of friction that is equal to μN is _________ ___________.
Kinetic Friction
When a car skids to a stop, the predominant form of friction slowing the car is __________ _________.
Kinetic Friction
The force that keeps you from falling to the floor when you sit in a chair is the ________ _________.
Normal Force
the only Force besides gravity affecting hanging block is ________.
Tension
When an object is accelerating, how does the apparent weight compare with the actual weight?
The apparent weight is greater than or less than the actual weight, depending on the direction of acceleration.
A block is on an incline. What is the relationship between the normal force and the gravitational force?
The normal force is less than the gravitational force.
The apparent weight is ...
The weight a scale records
An ideal string does _not_ affect a block's acceleration due to gravity because _______________________.
They have no mass.
The friction that makes jogging possible is called _______.
Traction
Coordinate systems are _always_ chosen within a frame of reference.
True
For an object resting on an incline, the normal force is equal in magnitude of the y-component of the object.
True
If a free-body diagram consists of a system of two hanging blocks, one hanging from the other, and the top block is hanging from a fixed surface, then there are only two forces acting on the system.
True
In a free-body diagram, forces that a system is exerting are _not_ shown.
True
It usually requires more force to get a car to start moving than it does to keep it moving.
True
Static friction has a range of values for any two materials.
True
The coefficient of friction is a a scalar quantity.
True
The normal force and the frictional force are related.
True
Traction makes walking possible.
True
*Which of the following is _not_ a characteristic of an ideal string?* a. Ideal strings have mass. b. Ideal strings have no stretch. c. Ideal strings do not exert pushes. d. Forces are exerted only in line with the string.
a. Ideal strings have mass.
Which type of friction is involved in the motionless tires of a car parked on a hill? a. traction b. rolling friction c. static friction d. kinetic friction
a. traction & c. static friction
*Which statement about friction is true?* a. Friction acts perpendicular to the surfaces that are sliding over one another. b. Friction is a force that opposes the relative motion of the two surfaces in contact. c. Friction is dependent on the area of contact. d. Friction acts in the same direction as that of the relative motion.
b. Friction is a force that opposes the relative motion of the two surfaces in contact.
*Which of the following is _not_ a characteristic of an ideal pulley?* a. The axle is frictionless. b. The pulley must be anchored to an immovable surface. c. The motion of the string around the wheel is frictionless. d. The pulley changes the direction of forces without diminishing the magnitude of those forces.
b. The pulley must be anchored to an immovable surface.
Which statement about kinetic friction is _not_ true? a. It is independent of sliding friction. b. It is directly proportional to the normal force. c. It is perpendicular to the contact surface. d. It is usually less than static friction for a given object.
c. It is perpendicular to the contact surface.
*The following types of motion are made possible with friction except which one?* a. Rolling b. Walking c. Sliding d. Braking
c. Sliding
*Which of the following is _not_ an important step when analyzing inclined plane dynamics?* a. Assign coordinate systems to each system element. b. Resolve all the forces acting on the system into their components. c. Determine the maximum static friction possible. d. Calculate the mechanical advantage of the inclined plane.
d. Calculate the mechanical advantage of the inclined plane.
*Which one of the following is _not_ an example of kinetic friction?* a. Shoes rubbing the ground as someone walks b. Someone striking a match c. A soccer ball rolling into the goal d. Your friend trying to push a rock
d. Your friend trying to push a rock
How do Jersey barriers minimize injuries and damage due to car accidents? a. by blocking oncoming traffic b. by exerting the right force at the right angle c. by making highway divisions more visible d. all of the above
d. all of the above
When an object moves in an upward direction, apparent weight __________.
increases
The coefficient of friction ...
is different for different substances
The normal force ...
is perpendicular to the surface.
The direction of friction is __________ the direction of motion.
opposite
The mathematical definition of normal is __________ to a surface.
perpendicular
The x-axis must be __________ to the y-axis in any reference frame.
perpendicular
Ideal strings can exert only _________ __________ on objects.
pulling forces
An ideal string acting on a block ...
pulls in line with the string
The free-body diagram of the whole system is called the __________ __________.
world diagram