dynamics unit 2 Flashcards
Force
a push or pull
Contact force
physical interaction between objects
- FT (Tension force)
- FN (Normal force)
- f (Frictional force)
Non-contact force
Fg (Gravitational force)
How does the direction of the net force and acceleration compare?
The direction of the net force and acceleration must be the same
if the net force is in the same direction as the velocity how is the object’s speed changing?
The object must be speeding up if the velocity and the net force point in the same direction
if the net force is in the opposite direction as the velocity how is the object’s speed changing?
The object must be slowing down if the velocity and the net force point in the opposite direction
if the net force is perpendicular to the velocity, what happens to the object?
The object turns without speeding up or slowing down
How do we combine multiple individual forces into the net force?
we find the x and y components of each individual force and then add all the x components together and add all the y components together.
In free fall, what is the only force acting on the object?
gravity
True/False: If more than gravity is acting on an object the acceleration is unlikely to be 9.8 m/s^2
true
Newton’s First Law
When the net force on an object is zero, the velocity of the object must be constant. This means a stationary object stays stationary, and a moving object will move in a straight line at a constant speed
Newton’s Second Law
the net force is equal to the mass times the acceleration. This is a vector equation which we break into the x and y parts. The sum of the x components of the forces is equal to the mass times the x acceleration. The sum of the y components of the forces is equal to the mass times the y acceleration.
Newton’s Third Law
Forces are interactions between two objects which both must equally feel the same magnitude of force but in the opposite direction.
What is friction?
Friction is the force that attempts to prevent one object sliding along another object. There is static friction which is used when the objects are not sliding relative to each other and kinetic friction when the two objects are sliding along each other.
How do you tell if you use static or kinetic friction?
Calculate the maximum static friction force (mu_static times the Normal force). If the force trying to make the object slide is less than the max static friction then the static friction exactly matches the force trying to make it slide thus preventing it from sliding. If the force is greater than the max static friction, then we use kinetic friction which is mu_kinetic times the Normal force and it is in the opposite direction as it is sliding.
If the question mentions that the object has a constant velocity what MUST be true about the net force?
If the object has a constant velocity, then the net force MUST be ZERO. This does NOT mean that there are no forces only that they must add up to zero (both in the x direction and the y direction)
if you graph the force of a spring vs the length of the spring, what is the slope?
spring constant
If you graph the force of a spring vs the length of the spring, what is the y intercept?
the y intercept is the length of the unstretched spring
a force probe or force sensor gives you this type of graph _________________.
force vs time
when you push an object along ground that has friction at a constant velocity, how does the pushing force compare to the frictional force?
They must be equal because constant velocity means the net force MUST be zero
True/False: The net force ALWAYS points in the direction of the acceleration
TRUE
When an object has no net force acting on it, the object is in ______________.
equilibrium
The units of force are the _______________.
newtons
When there is a net force acting on an object, then the velocity (never/sometimes/always) changes.
always
True/False: Static friction applies to both stationary and sliding objects.
false
True/False: An object in equilibrium must be stationary.
false
True/False: The only way an object can remain stationary is if there are no forces acting on it.
false
True/False: The normal force on an object is always equal to the weight of the object.
false
True/False: Only internal forces can change the velocity of the center of mass of a system.
false
True/False: For an object sitting on a table, the normal force is the reaction force to an object’s weight according to Newton’s 3rd law.
false
if the ground is tilted, we _____ the x and y axis so that x stays parallel to the ground and y is perpendicular to the ground
tilt/rotate
When an object is traveling in a circle at a constant speed, where must the net force point?
to the center
When a horse pulls a stationary cart forward so that it starts to move, the horse pulls with a force that is (greater than/equal to/less than) the force the cart pulls the horse with.
equal
There are two methods to add vectors such as forces, the first is the graphical method and the second is to break each vector into ________________ before adding.
components
If the velocity vector and the net force vector act anti-parallel (180o) to each other then the object must be _______________.
slowing down
In order for an object to turn, there must be a component of the net force that is ________________ to the velocity.
perpendicular
When determining if an object will slide, we compare the force that is trying to make the object slide to the _______________.
maximum static frictional force
True/False: If the net force acts perpendicular to an object’s velocity, the speed must remain constant.
true
If the left side of a spring is attached to a wall while the right side of the spring is attached to an object, then the force from the spring on the object is (ALWAYS/SOMETIMES/NEVER) pointed to the right.
sometimes
When a truck and a fly collide, the force on the truck from the fly is (GREATER THAN/LESS THAN/EQUAL TO) the force on the fly from the truck.
equal
True/False: Due to the action/reaction force concept of Newton’s 3rd Law, there must always be an even number of forces acting on an object.
false
When a rope or a chain is attached to an object, what kind of force is this?
tension
True/False: A larger mass planet always has a larger acceleration due to gravity.
false
what are the 3 things necessary for uniform circular motion?
net force points to the center of the circle; the net force and acceleration are perpendicular; a =v^2/r
If a force is perpendicular to the velocity of the object the amount of work it can do on the object is always
zero. In the work formula the cos(theta) would be zero making the work zero.
for an object traveling in uniform circular motion what is the direction of the velocity?
The velocity is tangent to the circle (which is perpendicular to the raid)
How much work is done by the force providing for the centripetal force for an object traveling in a circle?
zero
What is an example of a situation where the normal force on an object is equal to the object’s weight?
An object sitting on a table with nothing extra lifting it up or pushing it down.
What is an example of a situation where the normal force on an object is NOT equal to the object’s weight?
An object on a hill
