Acceleration Where Acceleration is in the same direction as the object’s change in velocity

Direction of ∆V example V1 = 40 mi/hr V2 = 20 mi/hr Because ∆V came out negative, the change in velocity is backward Therefore the object is accelerating backward

Acceleration always has a direction. We will not use the word decelerate to indicate direction

In what direction does a coin that is tossed straight up accelerate? It is always accelerating down

A change in velocity example using numbers V2= 10 m/s V3 = 30 m/s V1=30 m/s Its change in velocity is down, therefore it must be accelerating down-even on the way up.

All objects in free-fall, near the earth’s surface, accelerate down at 10 m/s/s if we disregard air friction Free-fall means that the only force acting on the object is gravity

What is the quarter’s acceleration at the top of its trajectory? When the quarter is here 10 m/s2 down

Acceleration is the rate at which an object’s velocity changes

Again, we see that the object is accelerating down V2 = 30 m/s V1=30 m/s

Another example-are we there yet? V1 = 0m/s V2 = 10 m/s down The change in velocity is down, therefore it is accelerating down.

Acceleration units Units are extremely important Memorize the facts on pg 33 and 34 of my solution manual

An example of an object moving at constant speed and changing velocity would be a car rounding a curve at constant speed There are no examples of an object moving at constant velocity with changing speed Remember-Velocity is the speed and direction of an object

What is the acceleration of an object that starts off at 0 km/hr and is moving at 100 km/hr 10 seconds later? forward

What is the acceleration of an object moving at a constant velocity of 100 km/hr? Objects moving at constant velocity cannot accelerate!

What is the distance fallen by an object in free-fall, 5 seconds after it is dropped? For free-fall:

If you throw an object down, its acceleration is 10m/s2 after it leaves your hand In this example, it will have an initial velocity greater than 0 m/s

Two traffic lanes side by side at a red light V = 0 m/s V= 5 mi/hr For you, the initial velocity is not 0 m/s

Instantaneous velocity equation Allows one to calculate the velocity at any given time

Newton’s first law of motion An object at rest will remain at rest and an object in motion will remain in motion at a constant velocity, unless an unbalance force is applied to it.

A force is a push or a pull in a particular direction It is a vector We will use Newtons as units of force Is a Newton

Add up all the forces acting on an object Add up all the forces acting on an object. If the sum is 0 Newtons, the object cannot accelerate It will remain at rest or continue to move at constant velocity

If an object accelerates, we know that there must be an unbalanced force applied to it The moon accelerates as it goes around the earth The earth accelerates as it goes around the sun