Give two mathematical examples of Newton's third law and how you get the solution

1) Any particle moving in a horizontal plane slowed by friction, deceleration = 32 μ

2) The particle moving by acceleration = P/m - 32μ OR The external force = ma + 32μm

Explanation:

* Lets revise Newton's Third Law:

- For every action there is a reaction, equal in magnitude and opposite

in direction.

- Examples:

# 1) A particle moving freely against friction in a horizontal plane

- When no external forces acts on the particle, then its equation of

motion is;

∵ ∑ forces in direction of motion = mass * acceleration

∵ No external force

∵ The friction force (F) = μR, where μ is coefficient of the frictional force

and R is the normal reaction of the weight of the particle on the

surface

∵ The frictional force is in opposite direction of the motion

∴ ∑ forces in the direction of motion = 0 - F

∴ 0 - F = mass * acceleration

- Substitute F by μR

∴ - μR = mass * acceleration

∵ R = mg where m is the mass of the particle and g is the acceleration

of gravity

∴ - μ (mg) = ma ⇒ a is the acceleration of motion

- By divide both sides by m

∴ - μ (g) = a

∵ The acceleration of gravity ≅ 32 feet/sec²

∴ a = - 32 μ

* Any particle moving in a horizontal plane slowed by friction,

deceleration = 32 μ

# 2) A particle moving under the action of an external force P in a

horizontal plane.

- When an external force P acts on the particle, then its equation

of motion is;

∵ ∑ forces in direction of motion = mass * acceleration

∵ The external force = P

∵ The friction force (F) = μR, where μ is coefficient of the frictional force

and R is the normal reaction of the weight of the particle on the

surface

∵ The frictional force is in opposite direction of the motion

∴ ∑ forces in the direction of motion = P - F

∴ P - F = mass * acceleration

- Substitute F by μR

∴ P - μR = mass * acceleration

∵ R = mg where m is the mass of the particle and g is the acceleration

of gravity

∴ P - μ (mg) = ma ⇒ a is the acceleration of motion

∵ The acceleration of gravity ≅ 32 feet/sec²

∴ P - 32μm = ma ⇒ (1)

- divide both side by m

∴ a = (P - 32μm) / m ⇒ divide the 2 terms in the bracket by m

∴ a = P/m - 32μ

* The particle moving by acceleration = P/m - 32μ

- If you want to fin the external force P use equation (1)

∵ P - 32μm = ma ⇒ add 32μm to both sides

∴ P = ma + 32μm

* The external force = ma + 32μm