Chapters 3 & 4 Flashcards
As you read this in your chair, how fast are you moving relative to the chair? Relative to the Sun?
You are not moving relative to the chair, but you are moving over 100,000 km/h relative to the Sun.
What two units of measurement are necessary for describing speed?
distance & time
s = d/t
What kind of speed is registered by an automobile speedometer?
Instantaneous Speed (speed at any instance)
How can you use the graph of velocity versus time to estimate the acceleration of the ball?
by estimating the value of the slope of the graph
In the video, Dr. Hewitt drops a book and a flat piece of paper together from the same height, and one object hits the ground before the other. Why does that object hit the ground first?
The heavier object–the book–hits the ground first because the other, lighter, object is more influenced by air resistance
what factors determine whether the air resistance experienced by a falling object will affect the motion of the object?
The area of the object in relation to the weight of the object determines the air resistance the object experiences. Objects having greater area but smaller weight experience greater effect of air resistance.
What relationship between distance traveled and time did Galileo discover for freely falling objects released from rest?
Galileo discovered that distance increased as the time squared.
what equation shows that the average speed of a rabbit that runs a distance of 36 m in a time of 3 s is 12 m/s
v = s/t
which equation shows that the acceleration of a hamster is 5 m/s2 when it increases its velocity from rest to 10 m/s in 2 s.
a = deltaV/t
Select the correct equations that show that a freely falling rock drops a distance of 80 m when it falls from rest for 4 s
s = g⋅t2/2 = (10m/s2)⋅(4s)2/2=80m
Acceleration is generally defined as the time rate of change of velocity. When can it be defined as the time rate of change of speed?
When moving in a straight line, the time rate of change of speed is acceleration.
What exactly is meant by a “freely falling” object?
An object in free fall falls under gravity alone with no friction.
A ball is tossed with enough speed straight up so that it is in the air several seconds. Assume upward direction is positive and downward is negative.
0 m/s
3 velocities (m/s)
v = square root of v2 + v2
velocity
speed & direction
~ vector quantity
constant velocity
(constant speed and direction) motion in a straight line at a constant speed
changing velocity
if either speed or direction or both changes, then velocity changes
How does acceleration depend on the net force?
Acceleration is inversely proportional to the net force
If Dr. Hewitt applies 3 N of force to keep the block moving at a steady rate, what must be the force of friction, and why?
Equal to 3 N, because the force of friction should exactly balance out the force Dr. Hewitt applies, so that there is no net force acting on the block.
What general rule can you conclude about the force needed to keep an object in motion at a steady rate?
The force that you need to apply to keep an object moving at a steady rate is equal to the force resisting the motion of the object.
Acceleration (m/s2) depends on
on the net force
To increase the acceleration of an object, you must increase the net force acting on it.
When you apply a force to an object, friction usually
reduces the net force and the resulting acceleration
the force of friction does not depend on
speed
mass
a measure of the inertia of a material object
~ resists acceleration
acceleration is__________ proportional to the mass
inversely; (if one value doubles, the other value halves)
Newton’s Second Law of Motion
The acceleration of an object is directly proportional to the net force acting on the object, is in the direction of the net force, and is inversely proportional to the mass of the object.
~ Acceleration ∼ net force / mass
Once the crate is sliding, how hard do you push to keep it moving at constant velocity?
You push with a force equal to and opposite the dynamic friction force.
Which is normally greater: static friction or sliding friction on the same object?
Static friction is normally greater than dynamic friction.
What is the weight of a 1-kilogram brick resting on a table?
10N
Mass v. Weight
~ shaking vs. pull of gravity
~ balance vs. scale
An object at rest cannot remain at rest unless which of the following holds?
If there is a net force acting on a body, regardless of whether it is a constant force, the body accelerates. If the body is at rest and the net force acting on it is zero, then it will remain at rest. The net force could be zero either because there are no forces acting on the body at all or because several forces are acting on the body but they all cancel out.
A massive block is being pulled along a horizontal frictionless surface by a constant horizontal force. The block must be __________.
Since there is a net force acting, the body does not move at a constant velocity, but it accelerates instead. However, the force acting on the body is constant. Hence, according to Newton’s 2nd law of motion, the acceleration of the body is also constant.
Why doesn’t a heavy object accelerate more than a light object when both are freely falling?
The ratio of the weight to mass is the same for all objects in the same locality.
Calculate the weight in newtons of a 2100-kg elephant.
W=mg
2100 x 9.8 = 20580N
What is the net force acting on a falling 1-kg ball if it encounters 2 N of air resistance?
8N
If the mass of a sliding block is tripled while a constant net force is applied, by how much does the acceleration change?
The acceleration is reduced to 1/3 of its original value
