c 4-5 Flashcards
Relationship between acceleration and net force?
Acceleration is directly proportional to net force
Static friction vs. sliding friction
Static friction is greater than sliding friction. Example: Tires that are locked up from braking provide less friction than tires that are rolling.
Relationship between mass and acceleration?
Inversely proportional - The same force applied to twice the mass produces half the acceleration.
How does mass relate to inertia?
The greater the mass, the greater the inertia
How is mass different than weight?
Mass is the quantity of matter in an object. It is also the measure of the inertia that an object exhibits in response to an effort to push/pull/change its state of motion. Weight is usually the force upon an object due to gravity.
Newton’s second law
Law of acceleration… When a net force acts on an object, the object will accelerate. 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
the rate at which velocity itself changes
Acceleration in regard to mass
a = Fnet/m, Fnet = m*a, m = Fnet/a Mass resists acceleration - inversly proportional - twice the mass produces half the acceleration, thrice the mass produces 1/3 the acceleration.
Why doesn’t a stack of two bricks fall faster than one brick?
Because the acceleration of an object depends not only on force, but on its resistance to motion (inertia). (Tw exerted on an object with twice the inertia produces the same acceleration as half the horce exerted on an object with half the inertia!)
Why would a feather and a coin fall at equal rates in a vacuum?
Because the ratios of force to mass for each are equal. (Not because forces of gravity are equal!!)
Terminal speed
The speed at which the acceleration of a falling object terminates because air resistance balances gravitational force.
Terminal velocity
Terminal speed with direction specified.
Who reaches the ground first? A lighter or heavier parachuter?
The heavier because they achieve a higher terminal speed. The lighter person hits terminal speed first. It takes the heavier person longer to reach terminal speed, and they will be moving faster when it is reached.
When does acceleration stop in a free falling object?
If and when air drag builds up equal to gravitational force.
Friction
Resistive force force that opposes the motion or attempted motion of an object
Kg
The fundamental unit of mass.
Newton
The SI unit of force. One newton is the force that will give an object of mass 1kg an acceleration of m/s2.
Kg
The SI unit of mass.
Newton’s third law
Law of action and reaction…
Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first. To every action there is always an opposed equal reaction.
Does a speeding missile possess force?
No! Force is not something an object has (like mass), but is part of an interaction between one object and another.
Third law - 5 things about action/reaction forces
- one force is the action, the other the reaction
- are co-pairs of a single interaction
- neither force exists without the other
- are equal in strength and opposite in direction
- always act on different objects.
Newton’s first law
Law of inertia…
An object at rest tends to remain at rest, an object in motion tends to remain in motion at a constant speed along a straight line path.
If zero netforce, velocity remains the same!
A free falling object gains? Does acceleration remain constant?
10 m/s Acceleration is constant! Always the same amount in each passing second.
Do force and velocity vectors combine together?
No. Only force with force and velocity with velocity
