Where did the idea of acceleration come from?

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Where did the idea of acceleration come from?

• This idea has been around for a long long time.

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People have been thinking about acceleration for
thousands of years.

• In the fourth century B.C. two Greek Scientists,
  Aristotle and Strato described free fall as
  acceleration.
• Youve seen free fall before!
• Ever seen a Base Jumper?
• These are the thrill seekers that get their kicks
  by jumping off of tall structures and
  experiencing the sensation of flight.
• Just take a look at the following video clip and
  youll see what I mean!

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What a Rush huh?

• Anyways back to acceleration.
• Units of acceleration can be confusing.
• Almost all of the units that you will use in this
  class will be in metric units.
• If we measure speed in Km/hr then the change in
  speed is going to be expressed in Km/hr as well!
• For example, 25 Km/hr is the difference between a
  speed of 40 Km/hr and 15 Km/hr

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What is the formula for finding Acceleration?

• The formula for finding acceleration is the
  change in speed divided by the change in time.
• Acceleration Speed/ Time
• The units would be units of speed over units of
  time.

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Now if you remember back to the constant for the
acceleration of gravity you saw a rather strange
unit associated with it.

• Do you first of all remember the constant for the
  acceleration of gravity?
• 9.8 or 10 m/sec2
• Where does that sec2 came from?
• Think of the following situation,
• If something is falling at a certain speed, 9.8
  or 10 m/sec you have to measure that change in
  speed by a change in time, with respect to
  gravity it is measured in seconds.
• Therefore according to the formula for
  acceleration, which is the change in speed over
  the change in time, this is how we get the sec2
  in the constant
• The speed is 9.8 or 10 m/sec and the time it
  takes to do this is 1 sec, this translates into
  9.8 m/sec/sec or 9.8 m/sec2

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Thats all nice but what in the H_ _ _ does it
mean?

• What that means is that when something is
  released and is falling that its speed is going
  to change.
• The speed will increase!
• The speed will increase every second by a factor
  of 9.8 or 10 m/sec.
• This speed will continue to increase until the
  opposing force of the air that it is pushing
  aside equals the rate at which it is
  accelerating.
• This translates into an acceleration of ZERO.
• This is also known as Terminal Velocity.
• This is the point at which a falling body no
  longer changes its speed but stays at that speed.
• It doesnt fall any faster.

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How fast is Terminal Velocity?

• That depends on several things
• The shape of the item.
• The more aerodynamic the greater the terminal
  velocity.
• That is because there is less air resistance
  working against gravity and that allows a greater
  speed.
• It also depends upon the temperature of the air.
• The warmer the air the greater the velocity.
• This is because of the fact that warm air is less
  dense than cold air and wont have a lot of air
  pressure to work against the falling body.
• Thus allowing it to fall faster
• And most importantly, the constant of gravity.
• NASA engineers need to know what the constant for
  gravitational acceleration is on the different
  planets that we send probes to.
• Some planets have a much higher constant for this
  acceleration.
• This is because of the fact that we want the
  probe to survive reentry.
• If it falls too fast the atmospheric resistance
  on the probe could cause enough friction to make
  the probe burn up.
• They want to slow these instruments down before
  they burn up!

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Remember that the force of gravity has a constant
acceleration.

• We normally call this the G force.
• Take a look at what this guy is experiencing!

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That idea of slowing something down has a special
name.

• When something changes its speed in a downward
  direction, that is to say it slows down, as well
  as has its time changing, we call it
  Deceleration.

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But always remember this,

• No matter which way the speed changes it is
  always a form of acceleration!

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What does acceleration look like on a graph?
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Here is constant Deceleration.
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Here are two different rates of acceleration.