2. Definition
Force: any push or pull on an object
(it's that simple)
….But be careful!
Commonly students will think forces
have to come from living or moving
things. Not true. Gravity pulls a chair to
the floor and the floor pushes back.
3. Forces can cause:
1) speeding up
2) slowing down
3) change in direction
IN OTHER WORDS FORCES CAN*
CAUSE: ACCELERATION
*(but they don’t always cause
acceleration!)
4. Balanced forces:
When all the
forces cancel
each other out=
no net change in
motion (no
acceleration!)
5. Unbalanced forces:
Two or more forces that work and
add together to change motion
(cause acceleration)
Example of a canoe being rowed on a
river on a windy day
http://rt210.sl.psu.edu/simulations/physlets/force_table.html
6. Vectors
Forces are vectors
Vectors are ____________with
______________
Which one is a vector: Speed or
Velocity?
7. Newtons
In the metric system, the unit of force is
the Newton.
It can be used to quantify the pull or
push of ANYTHING!
What is correct: To weigh something in
pounds, Newtons, or Kilograms?
8.
9. balanced forces
example:
You on a chair
you are pulled down by gravity and the
chair pushes back on your butt. Think
about it....If you sat on the hard chair for
three hours without moving, wouldn't
you feel the chair's push?
10. unbalanced forces
example:
a rocket taking off
the force of the
engines is
enough to
overcome gravity
and the rocket
accelerates off
the launch pad
11. Questions
Is it possible to have one balanced
force? If so, draw as a vector diagram.
Is it possible to have 2 balanced
forces? If so, draw as a vector diagram.
Is it possible to have 3 balanced
forces? If so, draw as a vector diagram.
12. More questions
Can an object be in motion with
balanced forces acting on it? Defend
your answer.
Can an object be stationary with
unbalanced forces acting on it? Defend
your answer.
13. More….
Can you predict the motion of this box?
Force: 5 N
14. Friction:
a force; it causes negative acceleration
(slows things down and makes them
stop) (Can it also aid positive
acceleration?)
it's mostly caused by: interaction of the
matter that is in contact
Also caused by differences in materials
that are in contact.
15. The Three Types of Friction
and Each One’s Properties
3 types Typical Examples
Relative
strength
Sliding Strongest Book pushed
on table
Rolling Medium Car wheels
Fluid Lowest Swimming or
flying
16. From mass to Force (Part II)
Mass:
Amount of Matter in an object
Something is hard to move if it
has more mass
Basically the “amount of stuff”
found in something
17. Inertia
Objects with
mass don’t like to
move
This property is
inertia
How is it
measured?
18. Weight
Weight is a ___________
Caused by ___________
All atoms are pulled by gravity, so
things with atoms have weight
19. Speed and Velocity
Rate of motion
Velocity includes direction
V= D/T (with direction)
Units: Meters per second
20. Momentum
When things move faster, they become
harder to stop
And when they are more massive they are
also harder to stop
Momentum is like “inertia in motion”
ρ=Mass times velocity
Momentum is not a force, but it takes a force
to stop momentum………
Units: Kilogram Meters per second
21. Acceleration
When speed or direction changes
Only a force can cause acceleration
Change in speed divided by time
Or Ending speed – Starting speed
Time
Units: Meters per second squared
22. Acceleration when falling
On earth this is at a rate of 9.8
m/s/s
This is a fast rate of acceleration
What affects this acceleration
during the fall?
23. Finally………Force
Any push or pull
Forces can accelerate a mass
Force equals mass times acceleration
F= MA
Units: Kilogram meters per second
squared (or Newtons)
24. Weight is a Force
On earth you calculate weight by
Multiplying mass (in Kg) times
acceleration due to gravity (9.8 m/s/s)
This will give you weight in Newtons
Weight= mg
If you wanna turn your mass into
weight….don’t forget to multiply by 9.8
(m/s/s)
