# Rotational motion

Today I was thinking a bit myself about circular motion and I come up with a doubt. Suppose we tie a string with a bob and then fix other end of the string with a support. Suppose the string is inextensible and if we give the bob a velocity then it will undergo a circular motion and the magnitude of its velocity will remain unchanged as the work done by the tension will be zero. But we can say the string is providing tension to the bob as the bob has the tendency to move forward straight which would have increased the length of the string, so to maintain its length it provides the tension in such a way that it's length remain fixed. The time of impact is very small because in the next moment it's velocity changes the direction so we can say that an impulse is given to the bob perpendicular to its motion to change its velocity but why it's magnitude doesn't change though the impulse is perpendicular

• What impact? Please explain the situation a little more (maybe with a diagram). Commented Nov 24, 2018 at 18:28
• Actually a diagram will be better but I dont know how to post a picture Commented Nov 24, 2018 at 18:36
• If you add a link to an online image, and someone can edit your post to embed it inside. Commented Nov 24, 2018 at 20:22