Download - Review velocity, acceleration and the conditions needed to cause

TODAY’S OUTCOMES:
FORCE, MOTION AND ENERGY
- Review velocity, acceleration and the
conditions needed to cause acceleration
- Observe and plot the change in
acceleration of a rolling object with
steepness
- Learn to calculate final speed from
average speed and acceleration
*Suppose we were on a bus, and had a carpenter’s level which we put on a level spot on
the floor. What would be bubble do
>when the bus starts moving? The bubble would shift to the front.
>when the bus is traveling down Euclid Avenue
at constant speed?
The bubble would be centered, since there is
no acceleration.
>when the bus stops? The bubble would shift to the rear.
>when the bus makes a right turn? The bubble would shift toward the right.
The bubble points in the direction of the acceleration, opposite
to the side on which you feel a force on your body.
acceleration direction
fluid left behind
due to inertia
The mass in the level is in the
fluid, NOT the bubble; the bubble
shifts in the opposite direction of
the fluid mass.
bubble shift
*If you were to move the level along the track you made for the rolling ball, taking the
same path as the ball and going the same speed, where would the bubble be centered and
where not? When the bubble was off-center, which direction would it be pointing?
Explain by drawing a diagram showing the track and the bubble level.
Diagrams will vary, but
the bubble will shift
toward the inside of the
turn.
Recall the example of a car making a sharp turn
on a banked curve
Which direction is the acceleration?
acceleration
Toward the inside of the turn
Which direction does the driver “feel” like he is
being “pulled” toward in the car?
The driver feels like he is “pulled” to the outside
Is there really a force pulling the driver outward? What direction is the force
really pointing, and why? No - the force of the banked road pushes the car
to the inside of the turn - the driver feels his body tending toward a straight
direction due to the Law of Inertia, and the moving car pulls him inward.
THOUGHT EXAMPLE #1: INERTIA AND ACCELERATION
Will you have problems pouring water into a glass - - when the train is sitting still? No
when the train is rolling at a constant speed of 100 mph?
No - as long as the speed is constant, the water should
pour into the glass just as it does when the train is still.
(The train, passenger, pitcher, water and glass are all
moving at the same velocity together!)
when the train is speeding up?
Yes - the water in mid-air will not accelerate with the train
because there is no force on it - it will splash toward the rear.
when the train is braking?
Yes - the water will keep moving forward as the train brakes.
THOUGHT EXAMPLE #2: INERTIA AND ACCELERATION
A 100 lb. person is standing on a bathroom scale
aboard a rocket ship.
The rocket ship is moving upward at a constant
speed of 100 mph.
bathroom
scale
How will the measured weight compare to that of
the weight measured on the ground?
The weight will be the same! All forces are still
balanced just as they are on the ground.
Under what conditions will the weight on the scale
change?
Only if/when there is an change in the speed
(acceleration) will the scale weight increase or
decrease. )
Does the person’s mass ever change? No!
Last Lab - An accelerating ball
You saw the ball did NOT keep the same speed it accelerated.
Are the forces on the ball all equal?
No - because the ball is changing velocity, the forces on
the ball are not equal - there is an external force.
WHAT YOU ARE EXPECTED TO KNOW:
- Velocity is both the speed and direction of an
object or body
- Any change in velocity is called an acceleration
- Acceleration only occurs when forces on an
object are not balanced
TODAY’S OUTCOMES:
FORCE, MOTION AND ENERGY
- Review velocity, acceleration and the
conditions needed to cause acceleration✓
- Observe and plot the change in
acceleration of a rolling object with
steepness
- Learn to calculate final speed from
average speed and acceleration