Abeka Physics Section 8.1 Flashcards
Explain how Newton’s Third and Second Law relate.
The equation F=ma implies that only one force is acting on an object. In reality, this force is the net force of the unbalanced forces. Thus, Newton’s second law of motion is often restated as Sigma(E)F=ma, where Sigma(E)F is the net force acting on the object.
Describe Newton’s Third Law
> “every action has an opposite and equal reaction”
Three important rules:
(1) forces always occur in action-reaction pairs
(2) action and reaction are always opposite, equal, and along the same line
(3) motion is caused by unbalanced forces acting on the same object
Explain equation Fw=mg
On basis of equation F=ma, the force required to accelerate an object of mass “m” at the rate “g” may be stated as follows: F=mg
In this case, F, the required force, can be considered the weight of the object. Therefore, the equation may be rewritten as Fw=mg, where Fw is weight.
Further useful equations from Newton’s second law
F1/a1=F2/a2
F1/m1=F2/m2
m1a1=m2a2
Describe Newton’s second law
> answers question of how much force must be used to accelerate a given body at a given rate
“force applied to a given body is proportional to the body’s acceleration: F=ka, where F is the net force, k is the proportionality constant, and a is the acceleration”
“for a given acceleration, the required force is proportional to the mass of the body: F=k’m, where k’ is proportionality constant (different from k)
F=ma (k=m, and k’=a)
the more mass, the greater the resistance to acceleration
Describe Inertial Mass
> inertial mass - object’s mass when measured at rest
>In F=ma, quantity “m” is often called inertial mass (rest mass)
Describe the reason for the tendencies of riding a roller coaster with Newton’s first law
A moment after the car follows the track’s down drop, the passenger feels as if his seat under him has dropped away. This occurs because his body tends to maintain the horizontal course it had before the track descended. Also, as the car rounds a curve, the passenger feels a “pull” away from inside the curve. This is due to the passenger’s inertia–his tendency to keep moving in a straight line while the car follows the curved track.
Describe Friction
> acts against every object in motion in the opposite direction to slow it down
When you slide a book across a table, eventually it stops sliding. This is caused by friction.
Describe Newton’s first law of motion
> often called law of inertia
“a push or pull is necessary to change the present state of any body of matter”
“the more mass a body has, the greater its inertia, and the more force is required to change its motion”
another way stated: “In the absence of an external force, every body maintains its present velocity. Thus, if a body’s velocity is zero, it remains at rest. If its velocity is nonzero in a particular direction and at the same speed.”
“a body cannot accelerate except under the influence of a force.”
Describe Inertia
> “a body’s tendency to maintain its velocity”
“a body in motion tends to move in a straight line at a constant speed, and a body at rest tends to stay at rest, unless acted upon by an outside force.”
this one word could be used to summarize Newton’s first law of motion
List the uses of Newton’s three laws of motion
> serve as a conceptual foundation of physics
>describe and predict motion of any material object
