What is Force

Static Friction

acts on objects that are not moving. Because of static friction, you must use extra force to start the motion of stationary objects. Once the object is moving, there is no longer any static friction. However, there is static friction. (Example: a heavy desk sitting on the floor)

Balanced Forces

are opposing forces of equal strength. In other words they are forces that are in opposite directions and equal in size. •When forces are balanced, there is no change in motion. •They have a Net Force of zero.

Opposing Forces

are two or more forces acting against each other. The resultant force is determined by subtracting the opposing forces. (The direction of the vector for the resultant force is determined by the largest of the opposing forces.) Objects such as walls and floors exert a force because every material is somewhat elastic.

Unbalanced Forces

cause motion or a change in motion. •When two forces are acting in the same direction, they add together. When the total force on an object is in one direction, the force is called unbalanced. An unbalanced force changes the motion of an object. They are opposing forces that have a Net Force that is not equal to zero. Unbalanced forces are not opposite and equal.

Contact Force

is a force exerted by an agent that TOUCHES the receiver

Non-Contact Force

is a force exerted by an agent that does NOT HAVE TO TOUCH the receiver.

Friction

is a force that opposes motion. •The strength of the force of friction depends on two factors: how hard the surfaces push together and the types of surfaces involved. acts in a direction opposite to the motion of the moving object. will cause a moving object to slow down and finally stop.

Force

is a push or a pull on an object. A force gives energy to an object - energy that can make an object start moving, stop moving, or change its movement. Forces can be exerted in the same direction or opposite direction. Force = Mass x Acceleration F = m x A Units of measure for force are kilogram-meters/second/second written kg-m/sec/sec or Newton (N)

Vector

is an arrow used to represent a force.The length of the arrow shows the amount of force. The longer the length of the arrow the greater the force it represents.The head of the arrow points in the direction the force is being exerted.

Air Resistnace

is an example of fluid friction caused by the particles that make up air. Air resistance makes a falling object slow down. It opposes an object's downward motion. You can think of an object being pushed up by this opposing force of air. As the object falls, the air resistance gradually becomes equal to the pull of gravity.The forces are then balanced. When forces are balanced, there is no acceleration. The object continues to fall, but it falls at a constant velocity.(Newton's First Law of Motion)

Newton (N)

is the SI (metric) unit of force. One kilogram of weight exerts the force of about 9.8 Newtons or 2.2 pounds.

Terminal Speed

is the greatest speed an object can reach while falling through air. (see above about air resistance and gravity becoming balanced and acceleration Sliding and Rolling Friction describe friction between two solid objects. All liquids and gases are fluids. Water, air, and oil are examples of fluids. Lubricants, such as oil, wax, and grease, which are slippery, change sliding friction, to fluid friction ths reducing friction.

Net Force

is the total of all forces. It is sometimes called the Resultant Force

Fulid Friction

is when an object passes over or through a fluid such as water, oil, or air. Fluid friction is easier to overcome than sliding friction. (Example: a boat sailing across a lake)

Rolling Friction

is when an object such as a wheel or ball rolls across a surface. Rolling friction is easier to overcome than sliding friction. (Example: a skateboard across a driveway)

Sliding Friction

is when two solid surfaces slide over (rubs) each other. (Example: pushing a box across the floor)

Gravity

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