Help, I'm confused about Velocity and Acceleration :(?

"Questions like

A car moving in a circle has a constant acceleration

A car slowing down has a decreasing velocity "

Those are not questions. They are statements. So I’m not sure what you are asking.

Velocity is a vector: it has a magnitude (speed) and a direction.

E.g. a velocity of ‘5m/s going north’ is a different velocity to ‘5m/s going east’; even though the speeds are the same.

A car can travel at a constant speed in a circle - but its velocity is not constant as its direction is constantly changing.

Acceleration is also a vector. In physics acceleration means how quickly velocity changes. So you get acceleration whenever velocity changes, which means when:

- speed changes (faster or slowe) and/or

- direction changes.

The direction of acceleration is tricky. Acceleration is always produced by a force; the direction of acceleration is the same as the direction of the force.

When something moves at a constant speed in a circle, the force making it go in a circle always points towards the centre - the force’s direction constantly changes (along a rotating radius) so acceleration is *not* constant.

If that helps!

Velocity is basically another word for speed that just takes into account the direction youre going.

Acceleration is a matter of if you are speeding up or slowing down while you moving.

So if a car is moving with a constant acceleration its moving at a constant rate over some time: 30->45 45->50 50->55 not 30->36 36->47 47->50 (In the 47-50 you can see your not accelerating at fast anymore).

A car slowing down has a decreasing velocity: I started at 50 mph now I am at 47 mph over some time and now I am at 30 mph. My acceleration will still be positive too, because that negative sign just depends on the direction. Yes, I am decelerating, but I am decelerating in a positive direction.

------->

Movement vector is speed in a specific direction. The sum of all vectors acting on an object is its velocity.

Acceleration is a change in velocity.

First of all, acceleration and velocity are quite independent. Yes, acceleration is the rate of change of velocity, but they don't need to have similar value. You can have vector velocity going right and vector acceleration going anywhere else.

If acceleration and velocity go in the same direction then you have a body that is accelerating.

If the 2 vectors go in opposite direction (velocity up and acceleration down for example) then the body is decelerating.

For example, when you throw a rock upwards, it starts with a certain vertical speed and an acceleration on the opposite direction due to gravity. The rock slows down due to gravity until it reaches the highest point and then start falling back. While falling back now it has downwards velocity and still downwards acceleration, so the vectors are parallel this time and the body accelerate (it starts with 0 speed in the highest point and reaches the floor with high speed again).

In circular motion instead you have a different setup. In uniform circular motion you have that the velocity is tangential to the circle, while you have centripetal acceleration, that is the vector acceleration is always pointing towards the center of the circle. In this scenario the acceleration doesn't change the speed, the body keeps rotating at the same rate, the role of the acceleration is that to make the body turns, it's what keeps the body in a circle, otherwise it would just go straight on a tangent line. You can also have accelerated circular motion, in this case you also have a tangent acceleration (and you still have the centripetal one), so the body can slow down or go faster while rotating, depending on the direction of the tangent acceleration vector (again, if parallel it moves faster, if opposite it moves slower).

Anyway there's not a general rule, they are indepentent, I covered the main scenarios (sadly with no figures, so maybe go check some on books/internet), but there is plenty of other possible cases, it's up to you to understand the basic concept and apply it to your problems.