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Forces
What is a force?A force is a push or pull from one
object to another object
Examples: Earth’s gravitational pull on us, you pushing a chair, a table supporting a book
What is a force?
All forces have both size and
direction
The unit of force is the Newton
(N)
What other concepts have both a
size and direction?
Net ForcesThe net force is the combination
all of the forces acting on the object
Whenever more than one force act on an object, always sum the forces into a single net force
Forces in the Same DirectionWhen forces act in the same
direction, you add the forces together
The net force will be in the same direction as the two original forces
F1= 5 N
F2= 3 N
Fnet= 8 N
Forces in the Opposite Direction
When two forces act in opposite directions, you subtract the smaller force from the larger force
The net force will be in the direction of the larger force
F2= 7 NF1= 2 N Fnet= 5 N
Balanced ForcesWhen the sum of the forces
acting on an object equals zero, the forces are said to be balanced.
Balanced forces are equal in size and opposite in direction
Balanced Forces- Newton’s 1st LawThere is no change in motion
when the forces are balanced.
A stationary object remains
stationary
A moving object has constant
velocity
Unbalanced ForcesWhen the sum of the forces are
non-zero, there are unbalanced forces acting on the object
Unbalanced forces produce a change in motion, so they are necessary to cause accelerated motion
The Big Idea
Unbalanced forces result in a net
forceThe net force causes the object
to accelerateThis acceleration can be
predicted and described
Force, Mass, and AccelerationAn object accelerates when a net
force acts upon it
The net force is equal to the mass times the acceleration:
F = maThis relationship is Newton’s 2nd
Law
Force, Mass, and AccelerationThe acceleration of the object
depends on both the forces acting on the object and the mass of the object
The net force and acceleration are always in the same direction!!
F2= 7 NF1= 2 N Fnet= 5 Na
Example 1How much force is needed to
accelerate a 30 kg scooter at a rate of 1 m/s2?
F = ma
F = (30 kg) x
(1m/s2)
F = 30 N
Example 2How much force is needed to
accelerate a 0.5 kg baseball at a rate of 0.04 m/s2?
F = ma
F = (0.5 kg) x (0.04
m/s2)
F = 0.2 N