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Ch. 12 Forces and Motion Part 1: Newton’s First Law of Motion (Law of Inertia)
What is Motion?
 Motion: An object moving at a speed
__________ ______ ______ in a given direction.
 Motion is caused by an outside force.
 A force is a ______ ___ ______.
Aristotle’s Classification of Motion
Natural Motion-
Give an example of unnatural motion:
Galileo’s Concept of Inertia
How did Galileo’s approach to the idea of motion differ from Aristotle’s?
Is a force required to KEEP an object in motion?
InertiaSpeed and Velocity
Speed - the rate of change of position (the distance traveled in a given time)
Speed = distance/time
VelocityConstant speed= steady speed
Constant Direction is a straight line
What is constant velocity?
Draw an example of constant direction.
You are walking down the aisle of a train at 1m/s.
Motion is Relative
What is your speed relative to the floor of the train?
 Everything is always moving
 When discussing motion, we
mean relative to something
else.
What is your speed relative to the ground if the train is
moving 50m/s when you are walking in the same direction
as the train?
What is your speed relative to the ground if you are walking
in the opposite direction of the train’s movement?
Sir Isaac Newton
 Newton is _____ ___ ____ _________ ______________ of all time
 Grew up on a farm then attended Cambridge University
 _____________ ____________, formulated and proved the
______________________________, ____________________________,
developed a theory of the nature of light
 Wrote 2 very important books
Newton’s 1st Law: Law of Inertia
 Built on Galileo’s findings.
 Every object continues in a ___________________, or in a state of motion in a straight line at
constant speed, unless it is ____________________________________________________
exerted upon it.
 An object moves by its own ____________.
Why will a coin fall straight into a cup even though the card is removed?
Net Force Combination of All Forces that Act on an Object
 _________ _________ objects do not speed up,
slow down, or change direction
 Net Force= ______________________ acting on an
object
 ____________ (N)- scientific unit for force
What causes objects to speed up, slow down or change
direction?
Arrows
Vector Quantity Velocity and other forces are shown with arrows
 The ____________________________________________ is the direction of the force.
 The ________ of the arrow represents magnitude (______ _______) of force
 So a small arrow means a small force in that direction
 Draw a picture of you standing on the floor and draw the force of gravity
Interacting Forces
• More than one force can act on an object
•
The sum of these forces is the net force
•
Remember: ___________________________
____________________________ of the force
•
•
•
______ arrows pointing in the same
direction
____________ arrows pointing in opposite directions
When the net force on an object is zero, it is said to be in equilibrium
What is Equilbrium?
 ___________ is a stretching force and can be measured using a weighing scale.
 Newtons (N), like pounds, are units of ___________________________________
In the picture of the sugar and spring scale, what is tension?
What force balances tension?
Equilibrium Rule-when the ____ _________ acting on an object is ______, it is in equilibrium.
 means sum of…so  F=0 means the sum of all forces equals zero!
If the girl on the rings hangs with her weight evenly, how would scale readings
in both supporting ropes compare with her weight?
The Support Force
If the book on your desk is in equilibrium (all forces=0), what forces are acting on the book?
Support ForceAn object is in equilibrium when:
1. It is not moving.
2. It is moving in a _____________ speed in a ___________________ path (constant velocity).
3. Two or more forces are acting on it
4. The forces on it add up to zero.
Forms of Equilibrium
1. Objects at _____ are in ___________ equilibrium,
2. Objects __________ at constant velocity are in ____________ equilibrium.
*Equilibrium is ____ _______- of ___ ___________.