Chapter 4 Force and Net Force

Warm-Up/Journal  Warm-up : Define in your own words, balanced and unbalanced  Journal : This weekend I…

Objectives  To be able to relate force and motion  To be able to explain what is meant by a net or unbalanced force

What is a Force?  A force is something capable of changing an objects state of motion.  The word “capable” is significant.  Accounts for balanced and unbalanced forces.

What is a Force?  A force may not necessarily produce a change in motion  If a force acts alone, the object will accelerate.

What is a Force?  Because it causes acceleration, Force is a vector.

What is a Force  What is a vector?  Provide some examples of vectors

Types of Forces: Contact  Applied  Friction  Tension  Air Resistance  Normal  Spring

Applied Force  Force “applied” to an object

Friction Force  Parallel to surface, resists motion

Tension Force  The tension force is the force that is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends. The tension force is directed along the length of the wire and pulls equally on the objects on the opposite ends of the wire.

Air Resistance  The air resistance is a special type of frictional force that acts upon objects as they travel through the air. The force of air resistance is often observed to oppose the motion of an object.

Sky Diving

Normal Force  The normal force is the support force exerted upon an object that is in contact with another stable object.  Acts perpendicular to the objects motion

Spring Force  The spring force is the force exerted by a compressed or stretched spring upon any object that is attached to it. An object that compresses or stretches a spring is always acted upon by a force that restores the object to its rest or equilibrium position.

Spring Force, Not just springs

Action-at-a distance Forces  Gravitational  Electrical (Discuss Later)  Magnetic (Discuss Later)

Gravitational  The force of gravity is the force with which the earth, moon, or other massively large object attracts another object towards itself.  By definition, this is the weight of the object. All objects upon earth experience a force of gravity that is directed "downward" towards the center of the earth.

Gravitational  The force of gravity on earth is always equal to the weight of the object as found by the equation:  Fgrav = m * g

What is Net Force?  The sum of all of the forces acting on an object.  Let’s start simple: 5 N 10 N

Net Force

Balanced Forces  Balanced forces happen when the net force equal zero, or the forces cancel each other out.  Examples  Gravity v. Normal  Applied v. Friction (non-moving and moving at constant velocity)  Tug of war

Unbalanced Forces  Occur when the net force is greater or less than zero and causes the object to have a change in motion.