Forces and Motions
Post on 23-Feb-2016
31 Views
Preview:
DESCRIPTION
Transcript
Forces and Motions
Chapter 13 – The Nature of Forces
Forces13.1 What is a Force? Anything that changes the state of rest or
motion of an object
It’s what causes ACCELERATION
Has magnitude and direction Therefore force is a vector
13.1 Force
A force can cause a resting object to move, or it can accelerate a moving object by changing the object’s speed or direction.
13.1 Combining Forces1) Balanced Forces:
5 N 5 N =
Equal forces in opposite directions cancel each other to produce no net force and therefore no movement.
0 N
Unbalanced ForcesResult when the net force acting on an object is NOT equal to zero
When an unbalanced force acts on an object, the object accelerates and moves in the direction of the net force
13.1 Combining Forces - Unbalanced
13.1 Combining Forces2) Adding Forces:
5 N 5 N 10 N =
Two forces, working in the same direction will add together to produce a net force larger than either original force.
3) Subtracting Forces:
13.1 Combining Forces
10 N 5 N 5 N =
Two forces working in opposite directions will subtract to produce a net force in the direction of the larger force.
There are two main types of friction: Static - keeps things “static” (i.e. stationary) Force resisting motion of an object at rest.
Ex- the force that is keeping this block from sliding downhill
Kinetic - friction that occurs with objects in motion.
Three types of kinetic friction: Sliding, Rolling and Fluid
Friction is a force that opposes motion between two surfaces that are in contact.
13.2 Friction
13.2 FrictionStatic Friction: works in the opposite direction to the intended motion. Object is at rest.
Rolling Friction: happens when an object rolls over a surface. Works opposite to the wheels’ motion.
Static friction Direction of motion
Rolling friction
Direction of motion
Seating Plan
Bassel
BeaAmaniIngrid
Alain
Mikel
Jenny
Chrissana
Demy
Anne Marie
Zeina
Patricia
Tara
Charles Elias
Mia
Sarah
ArthurRyan
Michel R
Richard
Paul
Michel B
Jad
Test
Physics (25 mins, April 4th) Acceleration Chapter 13.1 Chapter 13.2
Chemistry (25 mins, April 7th) Acids and Bases
(yes, that’s really it, so be really prepared)
13.2 Friction
Fluid Friction: happens when an object pushes fluid aside. The surfboard overcomes the fluid friction of the water.
Sliding Friction: acts between the sled and the snow, in the opposite direction to the sled.
FRICTION
STATIC SLIDING ROLLING FLUID
The friction between surfaces that are
stationary
force that exists when objects slide
past each other
force that exists when a round object
rolls over a flat surface (usually less than sliding friction)
force that exists when an object
moves through a fluid (air, water)
-a book sitting on a table
-rocks laying on the side of a mountain
-a hockey puck on ice
-a child going down a slide
-a roller blade on a sidewalk
-a bowling ball going down a bowling alley
-a plane flying through the air
-a swimmer swimming in a pool
is defined as is defined as is defined as is defined as
& an example is & an example is & an example is & an example is
Reducing Friction
A smooth surface does not have as much friction as a rough surface.
A lubricant, ball bearings or even air can be used to reduce friction.
13.2 Friction
It is an attractive force that pulls objects together.
13.3 GravityGravity is a natural phenomenon in which objects that have mass are attracted to one another.
13.3 GravityEarth’s gravity acts downward toward the
center of the Earth. There is an upward force that balances gravity.
Falling Objects
Terminal velocity: the constant velocity of a falling object when the force of air resistance is equal in magnitude & opposite in direction to the force of gravity.
Question: What other force is not present in a vacuum that would affect acceleration?
Answer = air resistance
In a vacuum, two objects would accelerate at the same rate,
regardless of their shape, because both are in free fall.
Free Fall: the motion of a body when only the force of gravity is acting on
the body.
Newton’s 1st Law of Motion According to Newton’s 1st Law, the state of motion of an object does not change as long as the net force is zero.
a) An object at rest will stay at rest unless a force acts on it.
b) An object in motion tends to stay in motion unless a force acts on it.
Ex: A soccer ball will remain at rest on the grass unless a force is acted on it. It will then stay in motion until another force acts on it.
This law is also called the “Law of Inertia”
Inertia: the tendency of an object to resist being moved or, if the object is moving, to resist a change in speed or direction until an outside force acts on the object.
Ex. In a car crash: You continue forward
because of inertia
Newton’s 2nd Law of Motion
Force equals mass times acceleration.
F = ma
Newton’s 2nd Law of Motion
Force = mass x acceleration Units: Newtons (kg·m/s2)
Acceleration of gravity on Earth = 9.8 m/s2
Acceleration of gravity on the Moon =1.6 m/s2
Weight = mass x acceleration due to gravity On Earth, weight ≈ mass x 10m/s2
On the Moon, weight ≈ 1/6 weight on Earth
Question 1: If you weigh 540N on Earth, how much would you
weigh on the Moon?
Question 2: A) If your mass is 42.5 kg on Earth, what is your
mass on the Moon? B) What would your weight on Earth be? C) What would your weight on the Moon be?
Newton’s 2nd Law of Motion
90 N540N x 1/6 =
42.5 kg!!!425 N
70.8 N
This will help you think about everything you have learned
Homework
Worksheet Newton’s 2nd LawQuestions 1-8 (see, it could be worse!)
Newton’s 3rd Law of MotionFor every action there is an equal and opposite
reaction.
Action: Earth pulls on you
Reaction: you pull on Earth
Action and Reaction on Different MassesConsider you and the Earth
Action: tire pushes on roadReaction: road pushes on tire
Action: rocket pushes on gases
Reaction: gases push on rocket
top related