Acceleration is ameasure of howfastvelocity changes. Acceleration is the change of velocitydivided by the change oftime. Acceleration is avector, and therefore includes both asize and adirection.Acceleration is also a change in speed and direction, there is:
Speed (a scalar quantity) (uses no direction)
- Distance is how far you traveled
- Time is how long it took you to travel
- Speed is how fast you are moving - Speed = Distance / Time
Velocity (a vector quantity) (uses a direction)
- Displacement is how much your position has changed in what direction
- Velocity is how quickly your position is changing and in what direction
- Velocity = Displacement / Time
The measurement of how fast acceleration changes is calledjerk.
- An object was movingnorth at 10 meters per second. The object speeds up and now is moving north at 17meters persecond. The object has accelerated.
- Anapple is falling down. It starts falling at 0 meters per second. At the end of the first second, the apple is moving at 9.8 meters per second. The apple has accelerated. At the end of the second second, the apple is moving down at 19.6 meters per second. The apple has accelerated again.
- Jane is walkingeast at 3kilometers perhour. Jane's velocity does not change. Jane's acceleration iszero.
- Tom was walking east at 3 kilometers per hour. Tom turns and walkssouth at 3 kilometers per hour. Tom has had a nonzero acceleration.
- Sally was walking east at 3 kilometers per hour. Sally slows down. After, Sally walks east at 1.5 kilometers per hour. Sally has had a nonzero acceleration.
- Acceleration due to gravity
Acceleration is therate of change of thevelocity of an object. Acceleration
can be found by using:
where
is the velocity at the start
is the velocity at the end
is the time at the start
is the time at the end
Sometimes the change in velocity
is written as Δ
. Sometimes the change in time
is written as Δt.
In difficult situations, the acceleration can be calculated usingmathematics: incalculus, acceleration is thederivative of the velocity (with respect to time),
.
Acceleration has its ownunits of measurement. For example, if velocity is measured in meters per second, and if time is measured in seconds, then acceleration is measured in meters per second squared (m/s2).
Acceleration can bepositive ornegative. When the acceleration is negative (but the velocity does not change direction), it is sometimes called deceleration. For example, when a car brakes it decelerates. Physicists usually only use the word "acceleration".
Newton's laws of motion arerules for how thingsmove. These rules are called "laws ofmotion".Isaac Newton is thescientist who first wrote down the main laws of motion.According toNewton's Second Law of Motion, theforce something needs to accelerate an object depends on the object'smass (the amount of "stuff" the object is made from or how "heavy" it is).The formula of Newton's Second Law of Motion is
,where is the acceleration,
is the force, and
the mass. This formula is very well-known, and it is very important inphysics. Newton's Second Law of Motion, in short "Newton's Second Law", is often one of the first things that physics students learn.
Deceleration is negative or backwards acceleration. This means that something slows down instead of speeding up. For example, when a car brakes, it is decelerating.
