1. STATE EXPECTATIONS - FORCES
P3.1 – Objects can interact with each other by
direct contact (pushes, pulls, friction) or at a distance
(gravity, electromagnetic, nuclear)
P3.2 – Forces have magnitude and direction. The
net force on an object is the sum of all the
forces acting on the object. Objects change
their speed and/or direction only when a net
force is applied. If the net force on an object
is zero, there is no change in motion (Newton’s
First Law)

2. P3.4 – The change in speed and/or direction of
an object is proportional to the net force
and inversely proportional to the mass of the
object. The acceleration and net force are
always in the same direction. (2ND LAW)
P3.3 – Whenever one object exerts a force on
another object, a force equal in magnitude
and opposite in direction is exerted back
on the first object. (3RD LAW)

3. FORCES & NEWTON’S LAWS 1. A FORCE IS ANY PUSH OR PULL. FORCES CAN
CAUSE OBJECTS TO CHANGE DIRECTION, TO
START MOVING OR TO STOP MOVING. *FORCES
CHANGE MOTION, THEY DO NOT CAUSE MOTION!
2. FORCES ARE REPRESENTED BY VECTORS.
WHEN 2 FORCES ARE GIVEN IN THE SAME
DIRECTION, THE AMOUNT OF FORCE IS ADDED
TOGETHER.
3. WHEN 2 FORCES ACT IN OPPOSITE DIRECTIONS
THE AMOUNT OF FORCE IS FOUND BY
SUBTRACTING THE SMALLER FORCE FROM THE
LARGER FORCE.

4. 4. Net Force = The overall force acting on an
object after all of the forces are combined.
What is the net force here?
What is the net force here?
Why is the net force facing to the left?
Describe what is occurring in this picture.

5. 5. Balanced Forces occur when the net force is
zero. There is no change in motion.
6. Unbalanced forces occur when the net force
acting on an object is not zero. Unbalanced
forces cause objects to accelerate. *Remember
that accelerate has a scientific definition
applied here!

6. 7. FRICTION- A FORCE THAT ACTS IN THE
OPPOSITE DIRECTION OF A MOVING OBJECT.
-FRICTION CAN ARISE FROM TOUCHING
SURFACES, BUT AIR CAN ALSO CREATE
FRICTION (LIKE AGAINST A MOVING CAR).
-FRICTION CAUSES MOVING OBJECTS TO SLOW
DOWN AND EVENTUALLY STOP.

7. 8. SIR ISSAC NEWTON (1642-1727), DESCRIBED
THE RELATIONSHIP BETWEEN FORCE AND MOTION
IN HIS FAMOUS 3 LAWS OF MOTION.
9. INERTIA- THE TENDENCY FOR AN OBJECT AT
REST TO REMAIN AT REST OR OBJECTS IN MOTION
TEND TO REMAIN IN MOTION. HEAVIER OBJECTS
HAVE MORE INERTIA.
10. NEWTONS FIRST LAW - AN OBJECT AT REST WILL
REMAIN AT REST. AN OBJECT IN MOTION
WILL CONTINUE MOVING UNTIL ACTED UPON BY A
FORCE.
BALANCED FORCES!

10. Newton's 2nd Law

11. FORCE = MASS X ACCELERATION
11. NEWTON’S SECOND LAW -
FORCE = MASS X ACCELERATION
EX. THE MASS OF A BALL IS 12 KG. IT IS
ACCELERATING AT A RATE OF 2 M/SEC/SEC.
HOW MUCH FORCE DOES THE BALL EXERT?
STEP 1: F = M X A
STEP 2: F = 12KG X 2M/SEC/SEC
STEP 3: F= 24KGM/SEC/SEC
KGM/SEC/SEC = A NEWTON (N)

12. 12. NEWTON’S THIRD LAW- FOR EVERY ACTION
THERE IS AN EQUAL AND OPPOSITE REACTION.

13. How does a rocket liftoff?
A large mass of gases are expelled at a very high velocity from
the combustion chamber of the rocket engine through
specially designed nozzles. The velocity of the exhaust gases
is very high and as the gases are expelled, a change in the
momentum of these gases takes place in the time the propellant
takes to burn. This is the force causing the gases to be ejected.
By Newton's third law, this force has a reaction, in the opposite direction,
and this is the force, or thrust, that accelerates the rocket.

14. 11. Gravity - the force of attraction between 2
objects due to their mass.
-the more massive an object, the more
gravitational pull it has.
-objects fall to earth because of the pull of
earth’s gravity. An object’s acceleration
near the surface of the earth is 9.8m/sec/sec.

15. Notice the large and small rocks both have
the same acceleration!

16. -Which would hit the ground first: a feather or an elephant?
If you add air resistance, which would hit the
ground first: a feather or an elephant?
12. Weight and mass are not the same thing.
Mass = a measure of the quantity of matter in
an object.
Weight= mass X acceleration due to gravity
(9.8 m/sec/sec)