Chapter 4 physics

What can be concluded about the net force on a car moving left with constant velocity?

the net force on the car is zero

Condition required for an object remain at rest

the net force exerted on it is zero

newton’s 1st and 2nd laws (equilibrium)

if an object is at rest, the net force must be zero. (the upward normal force must equal the downward weight)

newton’s 3rd law ( action-reaction pairs)

action-reaction forces: are equal in magnitude, opposite in direction, act on different object.

Force =

mass* g(gravity)

Tension

(mass below P) * g

Newton’s 3rd law

states that a physical interaction always generates a pair of forces on the two interacting bodies

every force has one and only one 3rd law pair force

true

the two forces in each pair act in opposite direction

true

two forces in each pair always act on

different bodies

3rd law pair comes from

one single interaction, not mixed

the two forces of a 3rd law pair always act on different bodies

true

newton’s 3rd law guarantees equal

forces, but accelerations depend on mass

the force on the smaller moon due to the larger earth is

equal in magnitude but antiparallel to the force on the earth due to the moon

Elevator is moving upward at a constant speed, the spring scale will read the exactly the same as it does when everything is at rest

constant speed means zero acceleration. Newton’s laws say that only acceleration changes the apparent weight or the reading on a scale

Newton’s Second Law F =

m*a kg

A force is a push or a

pull

a force is an interaction between

two objects or between an object and its environment

a force is a

vector quantity, with magnitude and direction

types of forces: normal force n

when an object rests or pushes on a surface, the surface exerts a push on it that is directed perpendicular to the surface (normal force is a contact force)

Types of forces: friction force f

a surface may exert a friction force on an object, directed PARALLEL to the surface (is a contact force)

Types of forces: tension force T

a pulling force exerted on an object by a rope, cord, etc. (is a constat force)

Type of forces: weight

the pull of gravity on an object is a long-range force (a force that acts over a distance) (is a long-range force)

Length of vector shows the …

magnitude

the longer the vector,

the greater the force magnitude

superposition of forces

several forces acting at a point on an object have the same effect as their vector sum acting at the same point

Newto’s First Law

• - Equilibrium: object is rest or moving with constant velocity (straight line with constant speed)

  • - object to be in equilibrium, it must be acted on by no forces, or by several forces such that their vector sum - that is, the net force - is zero

Net Force Causes

Acceleration (accelerates in the direction of a net applied force )

When the net force is zero, the acceleration is

zero, and the pluck is equilibrium

When is Newton’s First Law Valid

• - Bus traveling on a straight road and speeding up

• - Roller skates on the bus (you move backwards)

inertial frame of reference

a frame of reference in which Newton’s first law is valid is

An object in uniform circular motion is accelerated toward the

center of the circle (net external force on the object must point toward the center of the circle)

acceleration a of an object is directly proportional to the

net external force F on the object

Doubling the net external force doubles the

acceleration

halfling the net external force halves the

acceleration

the acceleration of an object is inversely proportional to the

object’s mass if the net external force remains fixed

Applying the same net external force F to a second object and noting the acceleration allow us to measure the

mass

When the two objects are fastened together, the same method shows that their composite mass is the

sum of their individual masses

newton’s second law of motion

the acceleration of an object is directly proportional to the net external force acting on it, and inversely proportional to the mass of the object

Weight

of an object (on the earth) is gravitational force that the earth exerts on it

w = mg

the value of g depends on the

altitude

Falling object massm

Hanging object, mass m

Newton’s Third Law

The two forces have the same magnitude but opposite directions

Newton’s first law, equilibrium equation

Newton’s second law equation

Newton’s second law equation

w =

mg

Newton’s third law

R =