7. Torque and mechanical equilibrium

Question 1

What is inelastic collision?

Answer 1

An object of mass m1 hits another object of mass m2 and the two objects merge in the collision, forming a combined object that moves with a final velocity.

Question 2

What do you observe when m1»m2

Answer 2

• If m1 is really big, then m1+m2 will move at the same velocity as m1
• the final velocity is the same as the initial velocity

Question 3

What do you observe when m1

Answer 3

• If m2 is really big, m1 will merge with m2 and stay still

* the final velocity is 0

Question 4

Define impulse

Answer 4

• the change in an object’s momentum

* impulse = F∆t = ∆P

Question 5

direction of impulse

Answer 5

Direction of the net force

Question 6

How do we use impulse to our advantage?

Answer 6

•increasing the interaction time lowers the force applied

ie. airbags - change in momentum is slow, interacts with face for a long time upon collision and force on head is lowered

Question 7

Define torque

Answer 7

A measure of how much a force acting on an object causes that object to rotate

Question 8

How does the torque arise

Answer 8

Arises from the perpendicular component of the applied force

Question 9

Direction of torque

Answer 9

• Counterclockwise - positive torque

* clockwise - negative torque

Question 10

What factors does torque depend on?

Answer 10

• magnitude of the force
• distance from the axis of rotation to the point where the force is applied
• the angle between the force and a line drawn from the axis to the point where the force is applied

Question 11

What conditions must be true for a rigid body to be in equilibrium

Answer 11

• the net force acting on the object must be 0

* the net torque acting on the object about any pivot point must be 0

Question 12

What is a definition of a rigid body

Answer 12

• the distances bw any 2 parts of the object are fixed

* the angles between the lines connecting any 3 points of the object are fixed