mech 2: laws of motion

Newton’s first law

An object will remain at rest or continue moving at constant velocity unless acted upon by resultant force

Newton second law

The rate change of momentum of an object is directly proportional to the resultant force on the object, and in the direction of the resulting force

Newtons third Law

One body A exerts a force on body B, body B an equal and opposite force on body A

• What are characteristics of newtons third law

You must identify the action and reaction

Both are the same type of force for example, gravitational or contact force

The force will be equal in magnitude and opposite and direction and act along the same line of action

What is the definition for momentum and equation and units?

The product of mass and velocity (Direction is the same as velocity)

P=mv

No=kgms^-1

What is the equation generally used for Newton second law, Are there any other alternative equations?

Fr=change in momentum over change in time

Fr=m(v/t)=m(v-u)/t

When is the equation Fr=ma used during the Second law

This is a special case if the mass remains constant

How would you calculate the change of mass at a constant velocity in a pipe?

First calculate the volume = cross-sectional area x length (or length per unit time)

Then calculate the change and mass per unit time by using the equation m= row x volume (or volume over time)

Then substitute the equation that you got during the first Step into the second equation to calculate the change Of momentum per unit time

What is another equation for the resultant force using the density area and velocity?

Fr= change in p/change in t = row x area x velocity²

Impulse definition and equation and what is it equivalent to?

The product of force and time for which the force act

Impulse = Ft

Since Frt also equals momentum, impulse = change in momentum

How can you calculate the final velocity by mass and momentum?

Change in momentum/change in time = change in mv/change in t

Rearrange to make v the subject

What a way to increase the velocity

Have a longer time of contact or hitting the object harder/with more force

Conservation of momentum definition and equation

Within a closed System, the total momentum in any specified direction remains constant

Therefore, total momentum before = total momentum after

The force impacting on an object will be equal and opposite on the object being pushed

Mu=mv

What is a perfect elastic collision (coelesce)

What is an inelastic collision?

When the total kinetic Energy and momentum is conserved

When some are all kinetic energy is transferred to other forms like heat or sound and only momentum is conserved