Module 2 Dynamics (Part One) Unfinished.

Newton’s First Law states that…

An object at rest stays at rest, and an object in motion stays in motion, unless acted on by an external unbalanced force.

Newton’s Second Law states that…

F = ma, so acceleration =F/M. Acceleration is always in the direction of the resultant force.

Newton’s Third Law states that…

If an object A pushes with a force, F on another object, B, then object B pushes with a force of -F on object A. So forces come in pairs, equal in magnitude but opposite in direction.

If forces are balanced…

The object will move at constant velocity.

If the forces are unbalanced…

The body will accelerate in the direction of the net force.

Weight =

Mass x Gravity

The higher the objects mass/inertia…

The harder it is to change its motion.

If F = ma, how do we manipulate it to find a? Additionally, how do we find m?

a = F/m and m = F/a

How can we find velocity using a = v-u/t

v = u + at

How to resolve horizontal component?

(Adjacent to angle)

= F cos Ø

How to resolve vertical component?

(Opposite to angle)

= F sin Ø

For forces to be in equilibrium…

Net force must be zero.

So with vectors on a plane, the equilibrium triangle is drawn so the…

Resultant vector faces the opposite way (this makes all forces add to zero).

This means you have to…

Reverse direction of resultant force.

Where is theta?

Note that theta is also in the opposite corner to a normal vector triangle. It is at the base of the reversed resultant vector.

When finding net force between two seperate forces…

Resolve either into two horizontals or two verticals and add together accordingly.

When finding net force on an object with more than one force being applied, e.g four.

Add all the horizontals.

Add all the verticals.

Friction…

Friction is a force that acts in the opposite direction to the motion of an object.

Friction in setting of cars.

Net Force = Engine Thrust + Friction

μ = Friction Coefficient

Constant value.

Static Friction Coefficient

Maximum friction present to be overcome for the object to start moving.

Kinetic Friction Coefficient

Friction present throughout the objects motion.

Friction = μ x F_n

Friction Coefficient x Normal Force

On a horizontal plane normal force is…

Weight (mg)

Significance of the “Normal” force.

Refers to forces perpendicular to a surface.

On a slope F_i is…

Weight force acting down the incline.

mgsinθ

On a slope F_n = “Normal” Force

Perpendicular to incline.

mgcosθ

On a slope -F_n = “Normal Reaction Force due to Newton’s 3rd Law.

change sign of mgcosθ

On a slope F_f

μ x mg x cosθ

Similar to horizontal normal formula which is μmg which is usual formula.