2. ACCELERATION

3. What is Acceleration  The increase in the rate or speed of something

4. More Scientifically  We can define acceleration as the change in velocity per unit in time

5.  If an object is speeding up, we can say that it is accelerating, or going faster per unit in time  If an object is slowing down, we can say that it is decelerating, or going slower per unit in time

6. In the real world  Acceleration is very common. It is very rare for an object to start off at a certain velocity  In real life, to reach our desired velocity, we must accelerate

7. Examples:  Vehicles  Humans  Animals  Weather

8. Formula for Acceleration  Because we describe it as the change in velocity per unit in time, the formula for acceleration is: a = Δv / Δ t

9.  Recall: Velocity is measured in m/s and time is measured in s  So, our unit of measurement for acceleration is m/s/s or m/s²

10. Example  A constant force changes the speed of a car from 8 m/s to 20 m/s in 4s. What is average acceleration? + v 1 = +8 m/s t = 4 s v 2 = +20 m/s Force

11. Example (Continued): What is the average acceleration of the car? Recall definition of average acceleration. + v 1 = +8 m/s t = 4 s v 2 = +20 m/s Force

12. A wagon moving east at 20 m/s encounters a very strong head-wind, causing it to change directions. After 5 s, it is traveling west at 5 m/s. What is the average acceleration? (Be careful of signs.) + Force v o = +20 m/s v f = -5 m/s E Example

13. A wagon moving east at 20 m/s encounters a head-wind, causing it to change directions. Five seconds later, it is traveling west at 5 m/s. What is the average acceleration? Choose the eastward direction as positive. Initial velocity, v o = +20 m/s, east (+) Final velocity, v f = -5 m/s, west (-) The change in velocity,  v = v f - v 0  v = (-5 m/s) - (+20 m/s) = -25 m/s Choose the eastward direction as positive. Initial velocity, v o = +20 m/s, east (+) Final velocity, v f = -5 m/s, west (-) The change in velocity,  v = v f - v 0  v = (-5 m/s) - (+20 m/s) = -25 m/s Example Cont

14. a avg = a avg = = vvttvvtt v f - v o t f - t o t f - t o a = a = a = a = -25 m/s 5 s 5 s a = - 5 m/s 2 Acceleration is directed to left, west (same as F). + Force v o = +20 m/s v f = -5 m/s E  v = (-5 m/s) - (+20 m/s) = -25 m/s

15. GRAVITY

16. What is Gravity?  The force by which objects tend to fall towards the centre of the earth

17. What is Gravity?  Gravity is what holds the planets in orbit around the Sun and what keeps the Moon in orbit around Earth.  The closer you are to an object, the stronger its gravitational pull is.

18. What is Gravity?  How much gravity an object has depends on how big it is.  To be specific, how much mass it has.

19. Who discovered gravity?  The first person who dropped something heavy on their toe knew something was going on, but gravity was first mathematically described by the scientist Isaac Newton.  His theory is called Newton's law of universal gravitation.  Later, Albert Einstein would make some improvements on this theory in his theory of relativity.Albert Einstein

20. What is the rate of gravity?  For the purposes of calculations on Earth, objects fall at a rate of 9.80m/s² 80

21. Acceleration Due to Gravity  Every object on the earth experiences a common force: the force due to gravity.  This force is always directed toward the center of the earth (downward).  The acceleration due to gravity is relatively constant near the Earth’s surface.  Every object on the earth experiences a common force: the force due to gravity.  This force is always directed toward the center of the earth (downward).  The acceleration due to gravity is relatively constant near the Earth’s surface. Earth Wg

22. Gravitational Acceleration  In a vacuum, all objects fall with same acceleration.  Equations for constant acceleration apply as usual.  Near the Earth’s surface:  In a vacuum, all objects fall with same acceleration.  Equations for constant acceleration apply as usual.  Near the Earth’s surface: a = g = 9.80 m/s 2 or 32 ft/s 2 Directed downward (usually negative). Directed downward (usually negative).