chapter 12: forces and motion

force

force

a ______ is a push or pull that acts on an object

motion

a force can cause a resting object to move, or it can accelerate/decelerate a moving object by changing the object’s _______ and/or direction

newton

force is measured in _____ abbreviated as N

kg times m/s2

1 N = 1 ________

add

forces in the same direction ______ together

subtract

forces in opposite directions ______ from each other

net

the _____ force is the overall force acting on an object after the forces are combined

0

when the net forces on an object are balanced, the net force is _____, and there is no change in the object’s motion

unbalanced

an ______ force results when the net force is NOT zero

moves

when an unbalanced force acts on an object, the object ________ in a specific direction

friction

_______ is a force that opposes the motion of objects that touch as they move past each other

static

________ friction is the friction force that acts on objects that are not moving

stationary

static friction exists on ______ objects

opposite

static friction always acts in the direction _______ to that of the applied force

sliding

________ friction is a force that opposes the direction of motion of a moving object as it slides over a surface

less

because it is easier to move an already moving object, sliding friction for an object is always ______ that static friction

rolling

________ friction is the friction force that acts on rolling objects

100-1000

for a given set of material, the force of rolling friction is about ___________ times less than the forces of sliding or static friction

fluid

______ friction opposes the motion of an object through fluid

air resistance

fluid friction acting on an object moving through the air is known as ____ ______

gravity

_______ is a force that acts between any two masses

attractive

gravity is an _____ force that pulls objects together

terminal velocity

eventually, the force of air resistance equals the force of gravity, and an object reaches ____________

curved

when you throw an object forward, you’ll notice that it actually follows a _______ path

projectile

this curved path is an example of ______ motion

gravity

the combination of a forward velocity plus ______ causes an object to follow a curved path

aristotle

_________ was a greek scientists and philosopher that lived in 384 bc-322 bc

galileo

________ was an italian scientist from 1564-1642

newton

______ started his work in 1665 on the basis of galileo

first

newton’s _______ law of motion states that the motion of an object does not change as long as the net force acting on the object is zero

law of inertia

newton’s first law of motion is often referred to as the ____________

resist

inertia is the tendency of an object to ______ a change in motion

mass

inertia is based on the _____ and the speed of an object

mass

newton’s second law of motion states that the acceleration of an object is equal to the net force acting on it divided by the object’s ________

a=f/m

newton’s second law equation

9.8m/s2

acceleration can also be due to gravity: _______

mass

_______ is the amount of matter in an object of the measure of the inertia

weight

_______ is the force of gravity acting on an object

w=mg

weight forumla

third

newton’s _____ law of motion states that whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object

reaction

whenever there is an action, there is an equal and opposite _______

direction

the reaction force is equal in size, but opposite in ______ to the action force

momentum

_______ is the product of an object’s mass to its velocity

more

the ______ the momentum something has, the harder it will be for that object to come to a stop

conservation

the law of _______ of momentum states if no outside force acts on the system, then the total momentum of the system does not change

when bat hits ball

when brushing your hair with a hairbrush

describe examples of force

newton (N)

identify appropriate SI units used to measure force

the forces acting on an object have equal strength and act in opposite directions, they are balanced. These forces cancel out one another, and the motion of the object they are acting on remains unchanged. When the forces acting on an object are unbalanced, they do not cancel out one another.

explain how the motion of an object is affected when balanced and unbalanced forces act upon it

Static, sliding, and rolling friction occur between solid surfaces. Static friction is strongest, followed by sliding friction, and then rolling friction, which is weakest. Fluid friction occurs in fluids, which are liquids or gases

compare and contrast the four kinds of friction

Gravity causes objects to accelerate downward, whereas air resistance acts in the opposite direction and reduces acceleration

describe how earth’s gravity and air resistance affect falling objects

there is one force applied at the beginning on the trajectory, after which the only interference is from gravity

describe the path of a projectile motion

projectile is an object upon which the only force is gravity

identify the forces that produce projectile motion

every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force. This tendency to resist changes in a state of motion is inertia

describe newton’s first law of motion and its relation to inertia

the acceleration of an object depends upon two variables – the net force acting on the object and the mass of the object. acceleration of the body is directly proportional to the net force acting on the body and inversely proportional to the mass of the body

describe newton’s second law of motion and its use to calculate acceleration, force, and mass values

Weight is equal to the mass of the object (m) x the acceleration due to gravity (g)

relate the mass of an object to its weight

forces always act in equal but opposite pairs. Another way of saying this is for every action, there is an equal but opposite reaction. This means that when you push on a wall, the wall pushes back on you with a force equal in strength to the force you exerted

explain how action and reaction forces are related according to newton’s third law of motion

momentum(p) = mass(m)x velocity(v)

calculate the momentum of an object

the total momentum of the two objects before the collision is equal to the total momentum of the two objects after the collision

describe what happens when momentum is conserved during a collision