# PHYS 1111L Lecture Notes - Lecture 4: Parallelogram Law, Net Force

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ACCELERATION

Acceleration, in physics, is the rate of change of velocity of an object with respect to time.

An object's acceleration is the net result of any and all forces acting on the object, as

described by Newton's Second Law. The SI unit for acceleration is metre per second squared

(m s−2). Accelerations are vector quantities (they have magnitude and direction) and add

according to the parallelogram law. As a vector, the calculated net force is equal to the

product of the object's mass (a scalar quantity) and its acceleration.

For example, when a car starts from a standstill (zero relative velocity) and travels in a

straight line at increasing speeds, it is accelerating in the direction of travel. If the car

turns, an acceleration occurs toward the new direction. In this example, we can call the

forward acceleration of the car a "linear acceleration", which passengers in the car might

experience as a force pushing them back into their seats. When changing direction, we might

call this "non-linear acceleration", which passengers might experience as a sideways force.

If the speed of the car decreases, this is an acceleration in the opposite direction from the

direction of the vehicle, sometimes called deceleration.Passengers may experience

deceleration as a force lifting them forwards. Mathematically, there is no separate formula

for deceleration: both are changes in velocity. Each of these accelerations (linear, non-

linear, deceleration) might be felt by passengers until their velocity (speed and direction)

matches that of the car.

-ZeonGrooza

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