Force is an action that can make a change in the shape or motion of an object.

  • It’s a vector. It has a magnitude and direction.
  • It’s calculated by dynamometer.
  • Its symbol is F.
  • SI unit of force is Newton=N
  • It has an agent.(Agent is something that pushes, pulls or acts. Force needs an agent because it needs a cause.)
  • There are two types:
  1. Contact force: It’s caused by physical touch and interaction. For example, hitting a wall in contact force because the hand of man needs to touch the wall.Ekran Resmi 2015-03-25 22.09.54 kopya
  2. Long-range force: It doesn’t require any physical touch. For example, gravity doesn’t need to touch us in order to pull us. Another example is two magnets pulling each other which is magnetic force.Ekran Resmi 2015-03-25 22.09.54

Perpendicular and horizontal forces don’t affect each other.

Net force is the sum of all the forces acting on an object. It is also called the resultant force.Ekran Resmi 2015-03-25 22.09.38

Types of Forces

Weight:Scan 1

Earth’s gravitational force acting on an object. Its vector is ALWAYS downward, since the center of earth is underneath us.


  • m=mass
  • g=gravitational acceleration= 9.8N/kg=9.8m/s^2

Normal force:

It’s ALWAYS opposite of the direction of a force that is acting on a surface. It’s ALWAYS perpendicular to surface. The surface’s force acts on the agent(source of reaction) and acts like reaction. It’s symbol is n.yeni

Tension force:

If a string pulls an object, the string exerts a force called “Tension” on the object. Tension’s magnitude and direction is same for all parts of a string. It’s symbol is T. Always goes out of the object. When pulling an object if the pulling force increases, the tension’s magnitude increases, too.tension

Friction force:

If an object slides on a surface, it eventually stops. This is because of the friction force. Its symbol is f. Just like the normal force, it’s caused by the surface. But in contrary, it’s parallel to the surface. When the surface becomes rougher, the friction’s magnitude increases. Its formula is2Ekran Resmi 2015-03-25 22.10.17

  • Kinetic friction: It’s symbol is fk.Scan 2 kopya

If an object is sliding, the kinetic friction’s direction is opposite to the motion.

  • Static friction: It’s symbol is fs.

Just like kinetic friction its direction is opposite the motion. The force that doesn’t allow object to move, prevents the motion on surface. This happens before the motion starts.

The normal force is multiplied by coefficient of friction(depends on the surface). When a man pushing an object both forward and downward, it’s harder for object to move. Because the weight of the object is combined with the force the man is applying downward so of the normal force the surface is applying(the reaction) is greater.Ekran Resmi 2015-03-25 22.08.53

Newton’s First Law

If there’s no force acting on an object, two conditions are possible:

  1. If the object is not moving, it’ll stay still.
  2. If the object is moving, it’ll continue it’s motion with a constant speed.

In other words if there’s no net force acting on an object, because there’s no force to change it’s motion, the object’s motion will remain the same.

For other explanations and quizzes:

Newton’s Second Law

If there is a net force acting on the object, the object’s velocity will change.

Fnet=m.a =kg.m(meter)/s^2

  • m=mass
  • a=acceleration=v/t

Acceleration’s direction is the same with the net force’s direction.

1 kg.m(meter)/s^2= 1 N

For 1kg mass to accelerate at 1m/s^, 1N force is needed.2

Newton’s Third Law

Action-reaction law: If two objects interact with each other, their forces will act on each other. The first object exerts a force that is action. Second object’s respond to that action is reaction. Reaction is always equal in magnitude but opposite in direction to action.Ekran Resmi 2015-03-26 17.02.34Ekran Resmi 2015-03-25 22.06.56

Free Body Diagram

In free body diagrams all the forces acting on the object must be shown.Scan 18.33.03300px-Free_body.svg kopya



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