TEK: 6.8B
Force and Motion


Force is a strength or energy as an attribute of physical action or movement; it is a push or pull upon an object resulting from the object's interaction with the another object. Whenever there is an interaction between two objects, there is a force upon each of the objects. Force only exist as a result of an interaction.

Forces affect how objects move. They may cause motion; they may also slow, stop, or change direction of motion of an object that is already moving. Two natural force we have experienced are the force of gravity and magnetic forces.

Force Calculation: mass x acceleration

GRAVITY (force)

Every time you jump, you experience gravity. It pulls you back down to the ground. Without gravity, you'd float off into the atmosphere - along with all of the other matter on Earth.

You see gravity at work any time you drop a book, step on a scale or toss a ball up into the air. It's such a constant presence in our lives, we rarely marvel at the mystery of it - but even with several well-received theories out there, like attempting to explain why a book falls to the ground, they're still just theories. The mystery of gravity's pull is pretty much intact.


Magnetic force is an attraction or repulsion that arises between electricity charged particles because of their motion; the basic force responsible for the action of electric motors and the attraction of magnets for iron.  


Balance forces are two forces acting in opposite directions on an object, and equal in size. Anytime there is a balanced force on an abject, the object stays still or continues moving continues to move at the same speed and in the same direction. It is important to note that an object can be in motion even if there are no forces acting on it.


Forces that cause a change in motion of an object is called unbalanced forces. Unbalanced forces are not equal. suppose that one of the teams inn tug of war pulls harder than the other team. The forces would no longer be equal. One team would be able to pull the other team in the direction of the larger force.

ACCELERATION (force and motion)

Acceleration is the rate of change of velocity (speed and/or direction) of an object. An object's acceleration is the net result (final and overall result) of any and all forces acting on the object, as described by Newton's Second Law.

FRICTION (motion and force)

Friction is what happens when any two things rub against each other. These can be solid things, like your two hands rubbing together, your skis rubbing on the snow, or a hammer hitting a nail. They can be gases, like friction with the water slowing down your car, or liquids, like friction with the water slowing down a boat. Friction also has to do with force, because in order for friction to happen, their has to be a force applied to the object.


Motion is the act or process of moving or being moved; it also occurs by changing place or even position. Motion is typically described in terms of displacement, distance, acceleration, time, and speed.

A body in motion tend to remain in motion, and a body at rest tends to remain at rest, unless acted upon by an outside force. So, if an object is moving, its mass will tend to keep it in motion, and if something is at rest, its mass will tend to keep it at rest.

For every force and action, there is an equal and opposite reaction. This is what causes a cannon to recoil when it fires. The 'kick' from the firing of the ammunition is what makes the cannon jump backwards.

Inertia is a property of matter that causes it to resist changes in velocity (speed and/or direction). According to Newton's first law of motion, an object with a given velocity maintains that velocity unless acted on by an external force. Inertia is the property of matter that makes this law hold true.


Mechanical Equilibrium is a state was no physical changes occur. Whenever the net force of an object is zero, the object is in mechanical equilibrium; this is known as the equilibrium rule.

SPEED (motion)

Speed can be thought of as the rate at which an object covers a distance. A fast-moving object has a high speed and covers a large amount of distance in a short amount of time. Contrast this to a slow-moving object that has a low speed; it covers a smaller distance in the same amount of time. An object with no movement has zero amount of speed.

Speed calculation: distance / time


1. Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

2. The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma. Acceleration and force are vectors (as indicated by their symbols being displayed in slanted text); in this law the direction of the force vector is the same as the direction of the acceleration vector.

3. For every action there is an equal and opposite reaction.