If you want to be technically correct, then you never talk about "decelerate". That's a
word made up by people who have been taught that "accelerate" means "speed up", and
who are uncomfortable and unfulfilled until they have a word that means "slow down".
"Accelerate" means change speed or direction of motion. A car screeching to a stop,
and a car maintaining a steady speed on a curve, are both accelerating, because in both
cases, either the speed or the direction of the car's motion is changing.
In the case described in the question, the definition of the positive direction of motion is
entirely up to the observer. He could just as well choose the downward direction as the
positive direction for his observations and calculations.
Furthermore, if you want to be just slightly technical, there are very few occasions
when you ever have to resort to the confusing concept of a negative velocity. Velocity
is a positive speed in a direction. The only reason you would ever need to say that the
velocity is negative would occur if you had already stated the speed, and the direction
you were about to specify were exactly the direction that the speed is AWAY from.
Get your directions straight, and the negative goes away.
An object with negative acceleration is slowing down. Negative acceleration means that the velocity of the object is decreasing over time, causing it to decelerate or come to a stop.
The impact of negative force on an object's motion is that it can slow down or stop the object's movement. Negative force acts in the opposite direction of the object's motion, causing it to decelerate or come to a halt.
The car is slowing down
In this case, acceleration is positive. Negative acceleration would cause the object to slow down (decelerate.)
In physics, the force of gravity is typically considered a negative force because it acts in the opposite direction to the motion of the projectile. Gravity causes the projectile to decelerate and move downwards.
Deceleration or negative acceleration
An object with negative acceleration is slowing down. Negative acceleration means that the velocity of the object is decreasing over time, causing it to decelerate or come to a stop.
The impact of negative force on an object's motion is that it can slow down or stop the object's movement. Negative force acts in the opposite direction of the object's motion, causing it to decelerate or come to a halt.
technically zero is neither negative nor positive
The car is slowing down
Consider
Yes, zero is technically bigger than negative one.
Yes and no. Technically, infinity cannot be negative because it is an idea, not a number, but negative infinity is used in several mathematical equasions
Technically, yes. -3, a negative integer, can be written as -3/1 or -6/2 which are fractions.
No.
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The friction caused by the brakes causes the car to decelerate. This negative acceleration, in turn, causes a force to be applied to all those in the car. This is the lurch you feel.