Ch.4- Newton's Laws Of Motion

The tendency of things to resist changes in motion; things at rest tend to stay at rest & things moving tend to continue moving. • An object doesn't accelerate of itself; acceleration must be imposed against the objects inertia.

The quantity of matter in an object. More specifically, it is the measurement of the inertia or sluggishness that an object exhibits in response to any effort made to start it, stop it, or change in amy way its state of motion. • The more mass, the greater an objects inertia.

The force due to gravity on an object.

o Mass is more fundamental; it remains the same everywhere, whereas weight changes with location (it is less on the moon) • Mass & weight are directly proportional (but not equal); if an objects mass is doubled, so is its weight.

The fundamental SI unit of mass. One kilogram (kg) is the amount of mass in 1 liter of water at 4 ∞ C.

The SI unit of force. One newton (N) is the force that will give an object of mass 1 kg an acceleration of 1m/s^2.

The quantity of space an object occupies.

Any influence that can cause an object to be accelerated, measured in newtons (in pounds in the British system)

The state of an object or system of objects for which any impressed forces cancel to zero and no acceleration occurs. • Support Force = Weight (but in opposite directions) • Doesn't mean that velocity = 0; but rather that the object will maintain the velocity it happens to have . • Ex. if a book that weighs 15N is at rest on a table, the table must be pushing back with 15N of support (normal) force, in order for there to be no acceleration.

The resistive forces that arise to oppose the motion or attempted motion of an object past another with which it is in contact. • Static friction (what builds up until there's enough opposition to produce motion) is somewhat greater than sliding friction; it is more difficult to slide a crate from a position of rest than to keep it in motion once sliding. o Surface Friction does not depend on an object's speed or area of contact; (but does when moving through fluids).

The speed at which the acceleration of a falling object terminates because friction balances the weight. • Occurs when an object gains enough speed so that the force of air resistance = its weight. • net F = 0; A = 0; Constant V • Ex. a feather reaches terminal speed very fast, b/c it is very light compared to its relatively large SA.

• Same size chute means that air • B/c the heavier one has a greater terminal speed; he must fall faster, and longer, for air resistance against the chute to match his greater weight (means he continues to accelerate to greater speeds after the lighter one has already stopped)

• Straight-line paths off into space, as stated by the law of inertia. • They would no longer move in the divine circles held by ancient & medieval astronomy (Aristotle), b/c to move in this circular path requires the presence of a force.

If there is no net force, there can be no acceleration, and the velocity of the object must be constant. • Every material object continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.

When a net force is present, the object will accelerate in the forces direction. o 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. • (A = F/m); if acceleration is tripled, the net force is also tripled, and the mass will decrease by 1/3. • If mass is increased by the same amount & at the same time as the net force, there will be no change in the resulting acceleration; will still equal the original a.

o 50 N of friction pushes back in order to offset the applied force; constant V = 0 net force. o The crate will accelerate; this will cause the applied F > Frictional F & an unbalanced force = acceleration.

o A= g; if air friction is ignored, the net force = object's weight.

o Because the greater mass offsets the equally greater force; whereas force tends to accelerate things, mass tends to resist acceleration. o A = F/M = 2F/2M

• a < g • Net Force = Weight - Air resistance

• Size & Speed • The larger the surface area (perpendicular to the direction of motion), the larger the air friction. • The greater the speed, the greater the molecular force of impact by the air resistance; encounters more number of air molecules per second.

o Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first. • Ex. if we call the force on the bat when hitting a ball the action force, then the reaction force would be the backward force on the ball against the bat. • Neither force exists w/out the other- forces always come in pairs, both of which constitute the interaction btw diff. things. • Never cancel b/c they act on diff. objects. • These forces are always equal in magnitude, b/c any mass greater than its counter object, is proportionally offset by a decreased acceleration.