5. Newton's laws & free body diagrams

Question 1

what is the spring force?

Answer 1

the spring force is a restoring force in the opposite direction of the motion

Question 2

Drag force (Air) formula

Answer 2

R = 1/2DpAv^2

R= drag force magnitude
D = drag coefficient
p = density of mediums
A = cross-sectional area of the object
v = relative velocity with respect to the medium

Question 3

Viscous force (liquid) - for a sphere formula

Answer 3

F = 6⫪nrv
F = viscous force magnitude
n = viscosity of liquid
r = radius of spherical object
v = relative velocity with respect to the medium

Question 4

When is an object in translational equilibrium?

Answer 4

• if the net force that acts on an object is 0

* the objects stays at rest or moves without changing its velocity

Question 5

Newton’s 1st law

Answer 5

• Every object in a state of uniform motion will remain in that state of motion unless an external force acts on it
• ie. no net force no acceleration (the velocity remains constant)

Question 6

Newton’s 2nd law

Answer 6

• Force equals mass times acceleration

* Any net force results in an acceleration (ie. the velocity changes)

Question 7

Newton’s 3rd law

Answer 7

For every action there is an equal and opposite reaction

Question 8

When a sudden brake is applied in the car, why does your body move towards the front?

Answer 8

• the external force is applied to the car

* therefore according to Newton’s 1st law, you will continue moving forward with the same velocity

Question 9

What is an action-reaction pair?

Answer 9

• any 2 interacting objects exert equal but opposite forces upon each other
• such forces are called an interaction pair, or an action - reaction pair