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 A push or pull on an object. 
 Described by: 
•STRENGTH 
•DIRECTION 
 A force gives an object energy to: 
•STOP MOVING 
•START MOVING 
•CHANGE DIRECTION
 The SI unit for force is the 
 The symbol for Newton is 
 One Newton = about the force you exert to 
lift a lime. 
 Named after: 
NEWTON 
N 
Sir Isaac Newton (founder of 
physics)
 Contact Force 
 Non Contact Force
 A push or pull on one object by another that 
is touching it. 
 Contact forces can be: 
 Strong 
OR 
 Weak 
Example: 
FRICTION= force that opposes 
motion between two surfaces in 
contact.
 A force that one object can apply to another 
object without touching it. 
 Examples Include: 
 Gravity- universal attraction between all objects. 
 Magnetism- attracts and repels objects
 An attractive force that exists between all objects that 
have mass. 
◦ Weight is a measure of the force of gravity acting upon an 
object. 
 On EARTH the force of gravity = 9.8 m/s2 
 All objects fall to the Earth at an acceleration 
of 9.8m/s2 due to the force of gravity.
 The amount of matter in an object.
 Weight and mass are related, but ARE NOT the 
same. 
CHANGE GRAVITY 
 Weight can due to 
 Mass change 
DOES NOT
 can be used to show forces. 
ARROWS 
LENGTH 
 The of an arrow shows the 
of the force. 
STRENGTH 
DIRECTION 
 The that the arrow points 
shows the direction in which the 
FORCE WAS 
APPLIED 
LONGER 
 The stronger the force the the 
arrow.
 The combination of all the forces acting on an 
object. 
 To calculate the net force: 
◦ If the forces act in the same direction they are 
added together. 
◦ If forces act in opposite directions they are 
subtracted. 
DO THE MATH pg 191, #13. Do with shoulder partner.
 Forces acting on an object that combine and 
form a net force of ZERO. NO change in 
motion.
 Forces acting on an object that combine and 
form a net force that is not zero. 
 Unbalanced forces cause an object to move. 
 Forces moving in the same direction are 
ADDED 
 Forces moving in the opposite direction are 
SUBTRACTED
FORCE= MASS x ACCELERATION 
F= ma 
Force measured in NEWTONS 
Mass measured in KILOGRAMS 
Acceleration measured in M/S2 
DO THE MATH pg 195….RACE!
 Weight and mass are related, but ARE NOT the same. 
 Weight can due to 
CHANGE GRAVITY 
 Mass change 
DOES NOT 
F = 
Weight on Earth = 
M x A 
MASS x 9.8m/s2 (acceleration 
due to the force of gravity)