Question

how do our Arm bend and straight

Answer 1

ARM BEND BECOZ OF ELBOW. IN ELBOW THERE ARE HING JOINTS.

HING JOINTS :- SPECIAL BONES OR JOINTS WHICH ALLOWS MOVEMENT IN ONLY ONE DIRECTION.

HENCE ARMS BEND AND STRENGTHEN.

HOPE SO THIS HELPS U.

Answer 2

Two factors
1 the contraction and relaxation
Of biceps and triceps
2 due to the hinge joint present in the elbow