Name: _______________________________ Class: ____

12.1 Forces

Chapter 12Forces and Motion

What are we going to learn?• _____________________________________

_____________________________________

Misconceptions• A soccer ball sits _______________. You come along

and ____________, sending it _________ across the field. It eventually ________ to a _______. You _____________ a _________ to start it ___________, and then it ____________ all on its own, right?

• No!• _________ cause all __________ in _________. Just

as you __________ a __________ to the ball to __________ it up from ________, the ____________ applied a ________ to _________ it down to a _______. If the ground _________ apply a force to the ball, it would ________________ forever __________ slowing down or ______________.

Forced to Change• Misconception: __________________________________________________________________________• Fact: __________________________________________________________________________________

How are Forces Described?• Force – a _________________________________• When one __________ pushes or ________ another

________, the first object ________ a _________ on the ___________ object

• Ex: You exert a __________ on a computer ______ when you ___________

• Ex: You exert a ________ on a ________ when you pull it ________________________

• Force is _____________ by its _____________ and by the _____________ in which it acts

• ___________ to the _______ is a _______________ from ___________ to the __________

• The _____________ and _____________ can be represented by an ___________

• The arrow _________ in the ____________ of the ________

• The arrow _________ tells you the ___________ (ex: the ___________________, the _______________________)

• The ___________ of the force is ______________ in the SI unit called a _____________, after the scientist Sir ___________________

• _____________ is the force that ___________ a _______________ mass to _______________ at a rate of 1 meter per second each second __________

• A _________ can cause a ___________ object to ________, or it can _____________ a _________________ by ______________ the object’s ___________________________

How do Forces Affect Motion?• Often ____________________ force acts on an

_________ at the __________________• The _________________ of all the __________ on

an object is called the ______________• The net force _______________ if and _______ an

___________ will _________________• When the ____________ on an object are

_____________, the net force is ________ and there is ______________ in the object’s _________

• When an _________________________ acts on an object, the _____________________________

• You can ________ the ________________ on an object by ____________ together the ______________ of _____ the individual __________ acting on the object

• Look at the figure below

• The big dog pushes on the box with a force of 16 N to the right

• The small dog pushes on the box with a force of 10 N to the right

• The net force on the box is the sum of these forces• In the situation, there was a nonzero net force• A nonzero net force causes a change in the object’s

motion

What if the Forces on an Object are not acting in the same Direction?

• The big dog pushes with a force of 20 N• The small dog pushes with a force of 10 N• The dogs are pushing against each other

• When the forces on an object act in opposite directions, the strength of the net force is found by subtracting the strength of the smaller force (think negative) from the strength of the larger force (think positive)

• When forces act in opposite directions, the net force is in the same direction as the larger force

• In the example, the box will accelerate to the right

Let’s try a few examples...

• Use what you know about net force to describe the motion of the box in the figure. Assume the box starts at rest.

• 1. You pull on your dog’s leash to the right with a 12 N force. Your dog pulls to the left with a 6 N force. Sketch this situation, including labeled force arrows.

• 2. What is the net force on the leash? Calculate it. Draw and label it.

• What's the definition of balanced forces?________________________________________________________________________________________• What's the definition of unbalanced forces?________________________________________________________________________________________• When forces are unbalanced and in opposite

directions, what is the combined force equal to? What direction is it?

____________________________________________________________________________________________________________________________________

• Use your answers above to explain what happens in a tug-of-war stand-off.

________________________________________________________________________________________• Use your answers above to explain what happens

in a arm-wrestling stand-off.____________________________________________________________________________________________________________________________________• How is a tug-of-war stand-off similar to an arm-

wrestling stand-off?____________________________________________________________________________________________________________________________________

• How are the two stand-offs different?

____________________________________________________________________________________________________________________________________________________________

Friction• The _________ that _____________ exert on each

other when they ________________ each _________• Ex: If you _________ a ________ across a table, the

surface of the ____________________ the surface of the _________

Factors that Affect Friction• 2 ____________: ______________________________ involved how ________ the surfaces are

_______________________________

• Ex: The ______________________ is ___________ on a blocking _______

• If his coach wanted to ______________________ to move the sled, the coach could ____________________________ of the sled. ________________ the ____________ of the sled ________________ would ____________________ and make the sled __________________________.

• ___________ surfaces produce ________________ than __________________________

• Ex: if you ___________________________ together ______________, there would be _______________ than if you ___________ your __________________________________

• Friction _____________ when ___________________________ against each other

• Friction ________ in a _________________________ to the direction of the __________________ (opposes the motion of objects that touch as they move past each other)

• _______________ friction, a ____________ object __________________________ until it _________________________________________

• How could you make it easier moving heavy objects?_____________________________________________• What would happen to the football player if he

switched to a much heavier sled?__________________________________________________________________________________________

Types of Friction• There are ____ main types of _______________: ____________ friction _____________ friction _____________ friction ____________ friction

Static Friction• The friction force that _____________________________________________________________________

Sliding Friction• A force that _____________ an object’s

______________ of motion as it __________________________

Rolling Friction• The friction force that _________________________

Fluid Friction• This force _____________ an object’s

________________________________________• Ex: ______________________ that acts on an object

moving through the air

• Why is it more difficult to walk on ice than on the floor?__________________________________________________________________________________________• Which type of friction keeps your shoes from slipping

on the floor?_____________________________________________• Which type of friction keeps you skating on an icy

pond?__________________________________________________________________________________________• Which type of friction keeps you skating on an icy

pond?__________________________________________________________________________________________

Question...• How is friction between people like friction between

objects?____________________________________________________________________________________________________________________________________________________________________________________• Name 4 types of friction and give an example of each.____________________________________________________________________________________________________________________________________________________________________________________

• What types of friction occur between your bike tires and the ground when you ride over cement (__________), ride through a puddle (____________), and apply your brakes (_________________)?

• What is friction affected by?__________________________________________________________________________________________

Gravity• A ____________ that acts

_________________________________________ • It is an _____________________________• Earth’s _____________ acts ______________ toward

the _______________ of Earth

• What forces are acting on the skydiver?____________________________________________• Which force is greater?____________________________________________• How can you tell?________________________________________________________________________________________• How will the skydiver land safely?________________________________________________________________________________________

• Sir Isaac ___________ concluded that a ________________ objects ___________________ toward the __________ of Earth

• We are so used to _____________________ that we may not have thought about ___________________

• Newton published his __________________ in 1687.• What observations might you make today that would

lead you to the same conclusions about gravity?________________________________________________________________________________________

Universal Gravitation• Newton realized that __________ acts

______________ in the ____________, not just on Earth

• Ex: makes _______________________ to the ground keeps the ___________________________ Earth keeps all the ___________ in our solar system _______________________ the sun

Law of Universal Gravitation• The force of __________ acts ___________________ __________ in the universe that _________________• This means that _________________ in the universe

that _______________________________________

• You are _______________ not only ______________ but also to the ________, the _________________ in the solar system, and _________________________ around you

• __________ and the ___________ around you are _________________________ as well

• You do _______________ the ____________ among _________ objects because these __________ are _______________________ compared to the _________ of __________________________

• The ________________ force __________________ objects is ____________________ the force ________________________

• You ____________ only the ___________ of the ________________ gravitational ___________

• Ex: You ___________ your ______________ toward the ______ the way you ____________ toward Earth

Factors Affecting Gravity• ____ factors: __________ & ______________• Mass is a _____________ of the ________________

in an object (SI unit is the _______________)• The ______________ an object has, the

____________ the ___________________________ between it and other objects

• Ex: __________ gravitational force on nearby objects is __________ because the ___________________

_________. The ___________________ planets interact with a ______________ gravitational __________________ the _____________________ planets

• Gravitational _________ also _______________ the ______________ between the objects’ ___________

• Ex: As ______________________, gravitational _____________________. That’s why ________ can _______ a visible gravitational __________________ in your _______ and _____ on a pencil ________________.

• Ex: ______________________ would be able to perform _______ that are ______________________

• Gravitational _________ are _________ so golf ______ and baseballs can float or ___________________

• Give an example of another sport which would be affected by reduced gravitational force

_____________________________________________

What’s that Again?• The ____________ an object has, the ___________

its __________________________• The __________________________ is __________

one _________ and another, the _____________ the __________________________ between the objects

• Between which 2 objects is the gravitational force stronger, a robin and a worm or a bear and a cub? Why?

________________________________________________________________________________________

• Between which 2 objects is the gravitational force stronger, 2 apples in a fruit bowl or 2 apples on different branches of an apple tree? Why?

__________________________________________________________________________________________• In the solar system, which body exerts the most

gravitational force? Why?__________________________________________________________________________________________

• 1. Circle the object in the outermost orbit which experiences the greatest gravitational pull from the sun.

• 2. Planet B’s force arrow from the gravitational pull of the sun should be (longer/shorter) than planet A’s arrow.

• 3. Draw what a planet would look like it is was the same distance from the sun as Planet C but experienced a smaller gravitational pull from the sun.

Mass and Weight• ________ is sometimes ____________ with

__________• Mass is the ___________ of the

________________________ in an object• __________ is a _____________ of the

______________________ on an object• Ex: Your ________________________ displays the

______________________ Earth is ____________________

• What happens to the gravitational force between 2 objects when their masses are increased?

_____________________________________________

• What happens when the distance between the objects increases?

____________________________________________• If the mass of Earth increased, what would happen to

your weight?____________________________________________• What about your mass?____________________________________________• At any time, your _______ is the ________________

as it would be _______________________________• But your _________________ with the ___________

of the __________________________

• The _______ has a _________________________ at different places in the ________________________

• On the _________, he would weigh about _______ of what he ___________________

• On _______, he would weigh just over ______ of what he ____________________

The Ups and Downs of It...• __________ causes __________ to

________________________________• ________________________ acts in the

_____________________________ to the ________________ motion of ___________ and ________________________________________

Terminal Velocity• The ____________________ of a falling object when

the _______________________________________ the _____________________

Projectile Motion• The ________________ of an

____________________________________ and the __________________________________________ causes the ball to ____________________________

• _______________________ is a falling object’s ___________________ it is given a _______________________________