An object moving in a circle, is by definition, undergoing acceleration. Acceleration is a change in speed or direction. You do not have to slow down in order to move along a circular path, although you might want to if the tires on your car are bald or there is water on the road. :)
The example of an object going up and down and having a constant acceleration is exactly correct. Gravity acts at 9.81 m/s/s on the object regardless of the direction it is moving. On the way up, the object is slowing (assuming the only force acting on it is gravity) and on the way down it is speeding up.
This is a good question and requires some thought. I'm going to steal it for my classroom!
I don't think a circle is a change in direction. It is always going in a circle. A large object would have to change its acceleration in order to change direction dramatically. You have to slow down, if even by a bit, to change direction.
Sure. Although an object travelling in a circle is not a good example since it does not have constant acceleration (its acceleration vector is constantly changing direction.) A better example is what happens when you throw a ball straight up in the air. The constant acceleration of gravity causes it to slow down, stop and reverse it's direction.
Any change in either speed or direction is considered a change in velocity. Since acceleration is the rate of change in velocity, changing the direction of the velocity of an object, such as in circular motion, is a change in acceleration.
Another way to look at this is to recognize that force equals mass x acceleration, so a change in the force vector in magnitude or direction will change the acceleration, which is what happens in a circlè.
An object that moves straight up in a gravitational field is a good example of directional change without change in force or acceleration.
Yes, I believe it can.
Yes it can if it is moving in a circle.