Dynamics:Kinetics Force & Acceleration of a Particle

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Kinetics: Force & Acceleration on a Particle

Length: 07 Minutes 19 Seconds

## Kinetics

Kinetics is the study of force on a particle. Force is a product of Newton's Second Law Motion. "A particle acted upon by an unbalanced force F experiences and acceleration that has the same direction as the force and a magnitude that is directly proportional to the force." In other words force is a product of the particles mass and acceleration. Refer to equation 1.

(1)

## Graviational Effect

Your weight is not the same thing as your mass. Instead your weight is derived by you mass times the gravitational forces of the earth. Refer to equation 2.

(2)

The gravitational constant g can change depending on the altitude you are at, or if you are on a different planet. Now there is a way to calculate the gravitational constant g. Basically you have to realize that every object is attracted to one another and gives off its on gravitational field. This means you are pulling on the earth just as much as the earth is pulling on you. However, your mass is so small compared to the earth's mass; you basically have to no effect on the earth. To calculate the gravitational attraction between to particles equation 3 would be used.

(3)

G is the universal gravitational constant.

## Sum of Forces in Multiple Directions

Equation 1 doesn't apply to just one direction. It applies to all direction, along with rotational forces. From the sum of all the possible forces placed on the particle it would then be possible to determine the magnitude of force on the particle. Refer to equation 4.

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## Normal and Tangential Forces

Normal and tangential forces result from the normal and tangential accelerations that were calculated in kinematics of a particle; to calculate the normal and tangential forces equations 5 and 6.

(5)

(6)

This means that even if a particle has a constant velocity, if it is going around a curve it can still develop a normal force, and if it's accelerating around the curve it will have a normal force along with a tangential force.

## Inertial Effects

Inertial effects are the resistance a particle has to changes in acceleration. The best way to think of this is when you are in a car. If you accelerate fast you get pushed into the back of your seat, while if you stop fast you move forward and press against the seat belt. This is your body resisting changes in motion. This in turn will cause a force to press against you. So if the car accelerates to fast or decelerates to fast the human body could get damages due to large forces being placed on it. This is why cars have crumple zones; because those crumple zones will cause a lower deceleration of the car, which will put less force on the human body.

## Friction

There are two types of frictions that you should consider. They are static friction and kinetic friction. Static friction is the friction that keeps an object from moving, and the force resulting from it can be seen in equation 7. While kinetic friction is the friction that slows an object down once it starts moving. Refer to equation 8 to calculate the force caused by kinetic friction.

(7)

(8)

Notice that both static and dynamic friction are a production of the objects weight. This means that the coefficients of static friction and kinetic friction are unit less. Also, the coefficient of static friction is larger than the coefficient of kinetic friction, which means the resulting force from static friction is greater than the resulting force from kinetic friction.