Due Next Class:
U3.HW2
Do Now:
All (2 problems)
1. Walk in silently.
2. Grab a calculator and any papers for today.
3.
4.
Make sure your team is signed up!
Draw the FBD for a box being pulled to the left and
accelerating.
Created by M. Kelly
OBJECTS IN MOTION STAY IN MOTION!
By the end of today, IWBAT…
- Understand Newton’s 3rd Law
- calculate force and acceleration in
situations with normal and tension
force.
Why it matters in LIFE:
Part of being a
functional human
being is being able to
understand what’s
happening in the world
around you!
Why it matters in THIS CLASS:
Our Goal = 80%
Mastering today’s lesson (focused
participation, asking questions, etc)
is the first brick that will help us
reach our goal for this unit, and
eventually for the year
TEKS:
4(D) calculate the effect of forces on
objects, including the law of inertia,
the relationship between force and
acceleration, and the nature of force
pairs between objects;
4(E) develop and interpret free-body
force diagrams;
By the end of today, IWBAT…
-
Understand Newton’s 3rd Law
calculate force and acceleration
in situations with normal and
tension force.
Topic:
Newton’s 3rd Law,
Tension Force, &
Normal Force
NEWTON’S 3RD LAW!
DEMONSTRATE
Let’s demonstrate!
balloon & chairs
NEWTON’S 3RD LAW!
DEFINE
Forces always exist in
pairs!
For every action, there is
an EQUAL and
OPPOSITE reaction!
NEWTON’S 3RD LAW!
ACTION – REACTION PAIRS
For every action, there is an EQUAL and OPPOSITE reaction!
We call these
action-reaction
pairs
NEWTON’S 3RD LAW!
ACTION – REACTION PAIRS
ACTION:
Fins push DOWN on air
REACTION:
Air pushes UP on fins.
NEWTON’S 3RD LAW!
ACTION – REACTION PAIRS
ACTION:
Hammer pushes DOWN
on nail.
REACTION:
Nail pushes UP on hammer.
Fnail on hammer
F hammer on nail
NEWTON’S 3RD LAW!
ACTION – REACTION PAIRS
GUIDED PRACTICE!
Complete #1 & #2 on your Guided
Practice worksheet with your
shoulder partner.
NEWTON’S 3RD LAW!
ACTION – REACTION PAIRS
NORMAL FORCE
Normal force exists because of Newton’s 3rd
Law. The object’s weight pushes down on the
ground, so the ground pushes up on the
object!
FN is always ┴ to the surface the object is on.
REMEMBER
Applied Force – a push or a pull that is applied directly to the
object. Includes tension forces due to pulling!
Force of Gravity – equal to an object’s weight, the force caused
by acceleration of gravity (-9.8 m/s2).
Fg = m * -9.8m/s2
Normal Force –the perpendicular contact force that a surface
exerts on another surface, and is not always equal to the
object’s weight.
Friction Force –the contact force opposite of the direction of
motion that a surface exerts on another surface. (ex: static,
kinetic, air resistance, drag)
NEWTON’S 3RD LAW!
NORMAL FORCE
EXAMPLE
The Monster Book of Monsters
(a 2 kg book) sits on top of a
10 kg table.
1. Draw the FBD and calculate
the forces for the book.
2. Draw the FBD and calculate
the forces on the table.
NEWTON’S 3RD LAW!
NORMAL FORCE
YOU TRY
A 300 kg bear sits in a 5 kg
chair.
1.Draw the FBD and calculate
the forces for the bear.
2. Draw the FBD and calculate
the forces on the chair.
NEWTON’S 3RD LAW!
TENSION FORCE
EXAMPLE
You and your friends build a
treehouse with a pulley system.
You (weight = 800 N) stand at the
bottom and pull the rope taught
so the 5kg bucket is accelerating
at 0.5 m/s2.
1.Draw the FBD and calculate the
forces on the bucket.
2. Draw the FBD and calculate the
forces on you!
NEWTON’S 3RD LAW!
TENSION FORCE
EXAMPLE
A cat weighing 50N hangs at rest
from a 15 kg chandelier.
1.Draw the FBD and calculate the
forces on the cat.
2. Draw the FBD and calculate the
forces on the chandelier!
INDEPENDENT PRACTICE!
Procedure for IP time:
1) Silent work time
2) Work on #7, 8, and 9
Hierarchy of who to ask
1) Your brain
2) Your notes
3) Your partner (quiet whisper)
4) Ms. Kelly
EXIT TICKET
WHAT IT MIGHT LOOK LIKE ON A TEST:
1. A 6.0 kg block rests on top of a 7.0 kg block, which
rests on a horizontal table.
a) What is the force the top block exerts on the
bottom block?
b) What is the force the bottom block exerts on
the top block?
a. -59 N, (downward)
b. 59 N, (upward)