[susan53]

Grab is different - there's movement involved and it's fast and fairly desperate. It means to reach out your hand very quickly and then grip/grasp something - as in My little boy decided to ride his tricycle down the stairs. I tried to grab him but it was too late (true story unfortunately - we ended up in A+E).

Grasp also suggests movement - less desperate but equally strong : hearing He grasped my arm I understand He reached out and grasped my arm.

Grip on the other hand is static : She gripped the arms of the chair.

The Shorter Oxford Dictionary defines to grip as meaning to grasp and to grasp as meaning - guess what? But I'm not convinced. I'd suggest that grasp means to take (strong) hold of something whereas grip means to have (strong) hold of something

In any case, there are differences in metaphorical and idiomatic uses so they're not always interchangeable. Here are some that spring to mind :

1. Metaphorical :grasp = understand As in I find the idea difficult to grasp
2. Metaphorical : grip as in The film really gripped me = took up my whole attention
3. Idioms : grasp the nettle = face up to a problem ; get a grip on something = get control of something; grasp at straws = be reduced to relying on the weakest possibilities; to get to grips with something = to come to an understanding of something/ to get something under control; the objective is within our grasp = we can achieve the objective

Hope that helps