Newton's second law of motion Flashcards
True or false, any object accelerates when acted by a push or pull
true
What is a net force
a combination of forces that act on an object
True or false, acceleration is not dependent on net force
false
acceleration is dependent on net force
true or false: acceleration is directly proportional to the net force
true
acceleration ~ net force; or use the fish symbol like in engsci
what does directly proportional to mean?
that means the change in one is the same amount of change in the other
When does friction occur?
when surfaces slide or tend to slide over one another, a force of friction acts
What does friction do to the acceleration and net force of an object when a force is applied to the object?
friction:
- usually reduces the net force
- reduces the acceleration (usually)
What causes friction?
the irregularities in the surface of mutual contact, and depends on the kinds of material and how much they are pressed together
Where is the direction of friction force?
always in the direction of opposing motion
eg. an object sliding DOWN an incline experiences friction directed UP the incline
Does zero net force result in zero acceleration?
yes
true or false: no friction exists on a crate that sits at rest on a level floor
true
You push on a crate that sits on a smooth floor and it accelerates. If you apply four times the net force, how much greater will be the acceleration?
4X greater
this is because acceleration ~ net force
If you push with the same increased force on the same crate, but on a very rough floor, how will the acceleration compare to pushing on a smooth floor
it will have less acceleration because friction will reduce acceleration
Why is it important not to JAM the breaks to make the tires stop?
It is very important that you not jam on the brakes so as to make the tires lock in place. When tires lock, they slide, providing less friction than if they are made to roll to stop.
While the tire is rolling, its surface does not slide along the road surface, and friction is static friction - and therefore greater than sliding friction
What does the force of friction not dependent on?
speed
area of contact
What do you collectively call liquids and gases?
fluids
What do you call fluid friction?
drag
true or false: drag in a fluid depends on the nature of the fluid
true
true or false drag is greater in water than it is in air
true
does drag depend on speed and area of contact?
yes it does, unlike friction
True or false: for slow motion through water, drag is approximately proportional to the speed of the object
water drag ~ speed of object
true
True or false: in air, drag at most speeds is proportional to the square of the speed
true
eg. if an airplane doubles it speed, it encounters 4X the drag
- at very high speed however the simple rules break down when the fluid flow becomes erratic
What net force does a sliding crate experience when you exert a force of 110 N and friction between the crate and the floor is 100N?
10N in the direction of your push
A jumbo jet cruises at constant velocity of 1000 km/h when the thrusting force of its engines is a constant 100 000N. What is the acceleration of the jet? What is the force of air resistance on the jet?
The acceleration is 0 because the velocity is constant. Since the acceleration is zero, it follows from Newton’s second law…