# Query in mechanics

1. Mar 30, 2012

### mr newtein

Q1-if i apply a force on an object that object moves with acceleration does it mean object becomes like a force f=ma ?
Q2-is normal force a reaction to action of weight,since a force G.F acting on me so i must accelerate and mass*acc.=force so i am acting force on a floor(say) ,OR normal force is a force when two surfaces are in contact each one is acting a force on other and normal force is one of this force.
Q3-block1 is accelerating due to action of external force when it hits another block2, forces on block 2 are force due to block1 it was accelerating and m*a=f and contact force because for short period of time two surfaces will be in contact?

2. Mar 30, 2012

### chrisbaird

Q1: The object experiences a force according to f=ma, it does not become a force. It can exert a force on another object if it bumps into it later on.

Q2: Normal force typically refers to two rigid objects in contact and not in motion relative to each other in the direction normal to the surface where they contact. What gives rise to the normal force could be anything but in textbooks they usually mean it as the ground pushing up on an object as gravity pulls it down (This is not the reaction force. The reaction force of earth's gravity pulling me down is my gravity pulling the earth up.) The ground's normal force is ultimately electromagnetic forces binding the molecules of the ground together. Also, don't forget that the F in the equation F = ma is the total of all forces acting on the body with mass m. So a block sitting motionless on the ground has a = 0 and therefore F = 0 because the normal forces cancels out gravity.

Q3: For collisions of free bodies, you are better off using conservation of momentum and conservation of energy than forces/accelerations

3. Mar 30, 2012

### mr newtein

Thankkkkkkkkkkkkksssss buddy one more thing how a tension in a string occur and for numerical practice WILL i.e irodov will be best
best wishes from india