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AccelerationAcceleration – the rate of change of velocity
change in velocity over a change in time
aacceleration tf - ti
change in time
vf - vi
change in velocity
a
=
vf - vi tf - ii
Changerepresented by the Greek letter delta: Δequals the final condition
minus the initial conditionexample: ∆v = change in speedequation for change:
vfinal – vinitial
or… vf - vi ∆
Acceleration – cont’dAcceleration – the rate of change of velocity
change in velocity over a change in time
aacceleration ∆ t
change in time
∆vchange in velocity
a
=
∆v
∆ t
Acceleration – cont’dUnits for acceleration:
unit of distance / [unit of time]2
explanation: if unit for velocity: m/sif change in time measured in seconds = sunit = (m/s)/s = m/s2
for every second that passes, the object will accelerate this number of meters per second
Acceleration – cont’dIn physics, acceleration is not only an
increase, but also a decrease in velocity.Two ways to accelerate:
change speedspeed up
positive accelerationslow down
negative acceleration
Acceleration – cont’dIn physics, acceleration is not only an increase,
but also a decrease in velocity.Two ways to accelerate:
change directionyou can feel this acceleration as you turn a
corner in a car – your body is being “pushed” toward the outside of the curve
Acceleration can also be negative [deceleration] depending on the change in frame of reference
PracticeWhich has the greater acceleration, an airplane
that goes from 1000 km/h to 1005 km/h in 10 s, or a skateboard that goes from 0 to 5 km/h in 1 sec?
What is the acceleration of a race car that whizzes past you at a constant velocity 400 km/h?
If you’re running at 12 m/s and you accelerate at 0.33 m/s for 6 s, how fast are you going?
GravityGravity – the attraction of one
mass toward anotherdepends on the
masses of each andtheir distance fromone another
from our perspective…gravity is a constant acceleration toward the center of the earth
GravityGravity – the attraction of one mass toward
anotherdecreases over distance
explains why the moon has more of a gravitational effect [tides, etc] on the earth than the sun
Gravity – cont’dGalileo Galilei
experimented to find out the acceleration of free-falling objectsshowed that free-fall was constanthad difficulty showing this before using
inclined planesplane reduced force of gravity &
increased distance, but with same result
Galileo found greater accelerations for steeper inclines. The ball attains max acceleration when the incline is tipped vertically.
Air ResistanceAir resistance – the friction of air particles on
an object moving through itaccounts for varying speeds of falling
objects
Air Resistance – cont’dWithout air resistance, all objects fall with
the same constant acceleration due to gravity
RecapGalileo’s Observations:
a ball rolling down an inclined plane is moving with constant acceleration
greater accelerations for steeper planes, max acceleration when incline is tipped vertically
regardless of weight and size, when air resistance is small enough to be neglected, all objects fall with the same unchanging acceleration
Gravity – cont’dg = acceleration due to gravity
g = 9.8 m/s2 on earthg will change if
the object gets farther away from the center of the earth [distance change]
the object’s mass changes [but not in relation to the earth]
PracticeWhich of the following (if any) could not be
considered an “accelerator” in an automobile: gas pedal, brake pedal, steering wheel?
A sports car accelerates from 65 mph to 75 mph in 2 seconds while a minivan accelerates from 20 mph to 35 mph in 2 seconds.which has the greater acceleration?
[end]