Understanding Acceleration Direction in a Pendulum Swing

[ScullyX51]

Homework Statement

To understand that the direction of acceleration is in the direction of the change of the velocity, which is unrelated to the direction of the velocity.
The pendulum shown makes a full swing from -pi/4 to + pi/4. Ignore friction and assume that the string is massless. The eight labeled arrows represent directions to be referred to when answering the following questions.
What is the direction of vector A when the pendulum is at position 1?
What is the direction of vector A at the moment the pendulum passes position 2?What is the direction of vector A when the pendulum reaches position 3?

Homework Equations

I have no idea what equations I should be using here...I am very stuck and could use some hints to steer me in the right direction.

The Attempt at a Solution

All I know so far is that the acceleration is equal to the instantaneous rate of change in velocity.

 

[tiny-tim]

Hi ScullyX51!

What is the direction of vector A …

I'm really confused …

is "vector A" the A in the picture, or is it the acceleration?

 

[ScullyX51]

yes. I was very confused by that as well...but I am pretty sure vector a is referring to acceleration.

 

[tiny-tim]

yes. I was very confused by that as well...but I am pretty sure vector a is referring to acceleration.

ok … then the question is asking where the acceleration is when something moves in a circle.

You can work this out using r and θ, or i and j, or just by drawing a little triangle where two sides are the velocities at angles θ and θ + dθ, and the third side is the change in velocity.

 

[ScullyX51]

Thank you!