Hoop Marble Demo:
1. Sketch a picture of
the diagram to the
right in your notes.
2. Predict which path
you think the marble
will go if the hoop is
removed at the
instant the marble is
at position 1.
B
A
1
C
E
D
Hoop Marble Demo:
1. Sketch a picture of
the diagram to the
right in your notes.
2. Predict which path
you think the marble
will go if the hoop is
removed at the
instant the marble is
at position 1.
B
A
1
C
E
D
Hoop Marble Demo:
1. Draw an arrow on your
diagram that represents
the velocity at position 1
before the hoop is
removed.
2. Draw a different arrow
that represents the
direction the ring is
pushing on the marble at
position 1.
3. Use one of Newton’s Laws
to explain why the marble
travels on path C.
1
C
Hoop Marble Demo:
1. Draw an arrow on your
diagram that represents
the velocity at position 1
before the hoop is
removed.
2. Draw a different arrow
that represents the
direction the ring is
pushing on the marble at
position 1.
3. Use one of Newton’s Laws
to explain why the marble
travels on path C.
F
1
v
C
Imagine pushing a bowling ball…
What is the direction of acceleration?
In both cases:
• You have to stop the bowling ball from traveling upwards.
• You have to start the ball traveling to the left.
Imagine pushing a bowling ball…
What is the direction of acceleration?
In both cases:
• You have to stop the bowling ball from traveling upwards.
• You have to start the ball traveling to the left.
Broom Ball (Borling = Bowling +
Curling)
• You will be in a team of 3 or 4. but you have to go through
the 4 times.
• Each team member must use only the broom to get the
bowling ball from Box 1 to Box 2 or visa versa.
• You may hand off the broom once the ball has come to a
complete stop inside
• You may not touch the bowling ball in any way in the no
touch zone.
• Your team will be timed, team with the fastest time wins.
5 second penalty for any infraction.
• Horizontal pushes only, no touching the top of the ball.
Box 1
No-Touch
Zone
Box 2
TripleCross Zone
Corner
Broom Ball (Borling = Bowling +
Curling)
• You will be in a team of 3 or 4. but you have to go through
the 4 times.
• Each team member must use only the broom to get the
bowling ball from Box 1 to Box 2 or visa versa.
• You may hand off the broom once the ball has come to a
complete stop inside
• You may not touch the bowling ball in any way in the no
touch zone.
• Your team will be timed, team with the fastest time wins.
5 second penalty for any infraction.
• Horizontal pushes only, no touching the top of the ball.
Box 1
No-Touch
Zone
Box 2
TripleCross Zone
Corner
Force Perpendicular to motion
• A force perpendicular to an objects velocity
causes a change in direction, NOT speed.
• Think of it as constantly accelerating sideways.
• http://www.youtube.com/watch?v=3tNVOhtv
PEw
Force Diagram:
1. Draw a FBD
for the lawn
mower as
viewed from
the top.
2. Draw a FBD
for the lawn
mower as
viewed from
the back of
the mower.
Force Diagram:
1. Draw a FBD
for the lawn
mower as
viewed from
the top.
2. Draw a FBD
for the lawn
mower as
viewed from
the back of
the mower.
Fmow
T
f
N
T
W
Misconceptions of Circular motion and
the fictional centrifugal force
Misconceptions of Circular motion and
the fictional centrifugal force
What do we feel?
A car goes around a sharp corner.
Debunking the Centrifugal Force
Imagine you are riding in a fast car. The driver steps on the accelerator
and the car speeds up
• Which direction do you feel like you are being pushed?
• Which direction are you actually accelerating and being pushed?
Anti-gravity bucket?
• Why doesn’t the water fall out?
Anti-gravity bucket?
• Why doesn’t the water fall out?
In order for the bucket to go in a circle it
needs a force that acts toward the center
of that circle. At the top the FBD look like:
W T
The weight force and the tension both
act toward the center changing the
direction of the bucket’s (and water)
motion. The velocity is changing but
only in direction not in magnitude.
Right before the top the bucket (and
water) are traveling up. The force stops
it from going into the ceiling
Centripetal Force
Centripetal is the DIRECTION of the net force
BECAUSE THIS IS A NET FORCE YOU
CANNOT
DRAW IT ON A FORCE DIAGRAM.
It is always made up of other forces.
What force(s) are causing the
centripetal acceleration?
A ball tied to a string in swung around in a circle above
your head.
What force(s) are causing the
centripetal acceleration?
A ball tied to a string in swung around in a circle above
your head.
Tension
What force(s) are causing the
centripetal acceleration?
A car goes around a sharp corner.
What force(s) are causing the
centripetal acceleration?
A car goes around a sharp corner.
Friction
OH no!!! ICE!!!!
Which direction will the car go when it hits the
frictionless patch of ice?
A
ICE
B
C
D
OH no!!! ICE!!!!
Which direction will the car go when it hits the
frictionless patch of ice?
ICE
C
What force(s) are causing the
centripetal acceleration?
A satellite orbits around the Earth.
What force(s) are causing the
centripetal acceleration?
A satellite orbits around the Earth.
Gravity
What force(s) are causing the
centripetal acceleration?
A roller coaster cart travels up the side of a circular
loop.
What force(s) are causing the
centripetal acceleration?
A roller coaster cart travels up the side of a circular
loop.
Normal
What force(s) are causing the
centripetal acceleration?
A roller coaster cart travels upside-down at the top of
a circular loop.
What force(s) are causing the
centripetal acceleration?
A roller coaster cart travels upside-down at the top of
a circular loop.
Gravity
Normal
Centripetal Acceleration
• If there is a net force towards the inside of the circle then
there must be an acceleration.
࢜૛
ࢇࢉ =
࢘
• Where v is the linear velocity of the object around the
circle and r is the radius of the circle.
• Using Newton’s 2nd Law the Centripetal Force becomes:
Σࡲ = ࢓ࢇ
࢓࢜૛
Σࡲࢉ =
࢘