## FORCEBy: Rachel Killmer

### ISAAC NEWTON

• Lived from 1642 - 1727
• Discovered the binomial theorem at 18 years old.
• Discovered the law of universal gravitation.
• Stated the 3 laws of motion by 1665.

### FORCE

• Dynamics - The study of the effects of forces on matter.
• All changes in motion are the result of forces.
• Forces are what cause any objects to interact.
• The symbol for force is NEWTON (N)
• One Newton is equal to 1.0 kg x 1.0 m/s²

### KINDS OF FORCES

GRAVITAIONAL FORCE - a force of attraction that exists between all masses.

ELECTROMAGNETIC FORCE - the forces between charged particles.

STRONG NUCLEAR FORCE - holds the nucleus of an atom together.

WEAK NUCLEAR FORCE - a form of electromagnetic force that acts within the nucleus that is involved in breaking down nuclei.

### MASS AND WEIGHT

• Mass is the amount of matter in an object.
• Weight is the gravitational force exerted on an object.
• Weight is found using: W = mg
• W = Weight m = Mass g = acceleration of gravity (9.8 m/s²)
• Weight depends on location while mass does not.

### NEWTON'S FIRST LAW OF MOTION

AN OBJECT CONTINUES IN ITS STATE OF REST, OR OF UNIFORM MOTION IN A STRAIGHT LINE, UNLESS IT IS ACTED UPON BY AN UNBALANCED FORCE.

• Newton's first law is based off of inertia. (The tendency for an object to remain in its same state of motion.)

#### Example:

• If you kick a ball on Earth, eventually it will stop, because of friction, gravity, or air resistance on Earth.
• If you kick a ball in space, it would keep going forever, because there is no gravity, friction or air resistance in space.

### NEWTON'S SECOND LAW OF MOTION

WHEN AN UNBALANCED FORCE ACTS ON AN OBJECT, THE OBJECT WILL BE ACCELERATED. THE ACCELERATION WILL VARY DIRECTLY WITH THE UNBALANCED FORCE APPLIED AND WILL BE IN THE SAME DIRECTION AS THE APPLIED FORCE. IT WILL VARY INVERSELY WITH THE MASS OF THE OBJECT.

• The mathematical expression of Newton's second law is: F = ma
• F = Force m = Mass a = Acceleration

#### EXAMPLE:

An unbalanced force gives a 4.0 kg mass an acceleration of 6.0 m/s². What is the force applied to the object?

GIVEN: m = 4.0 kg a = 6.0 m/s² F = ? EQUATOIN: F = ma F = 4.0 kg x 6.0 m/s² F = 24.0 N

### FRICTION

• Friction is a force that opposes the motion of an object.
• STATIC FRICTION - resists the start of motion.
• SLIDING FRICTION - resists existing motion
• Static friction is always larger than sliding friction.
• To find friction, you use the equation: Ff = μFn
• Ff = Friction μ = coefficient of friction Fn = Normal Force
• Normal Force (Fn) of an object is numerically equal to that object's Weight (W)

### NET FORCE

• The vector sum of all forces acting on an object.
• To find Net Force, use the equation: Fn = Fa + Ff or Fn = Fa - W
• Fn = Net Force Fa = Applied Force Ff = Friction W = weight

### NEWTON'S THIRD LAW OF MOTION

EVERY FORCE IS ACCOMPANIED BY AN EQUAL AND OPPOSITE FORCE

• Forces are always in pairs.
• Every interaction involves two objects and two equal & opposite reactions.
• The action and reaction forces act on different objects.

#### Example:

If you hit a golf ball with a club, the club exerts a force and causes the ball to accelerate. The ball exerts an equal and opposite force on the club, accelerating the club in the opposite direction, and causing it to slow down.

### SUMMARY

• Isaac Newton
• Newton's First Law - An object in motion stays in motion; an object at rest stays at rest.
• Newton's Second Law - An unbalanced force causes acceleration.
• Newton's Third Law - Every action has an equal and opposite reaction.
• Dynamics
• 4 kinds of forces
• Difference between Mass and Weight
• Sliding Friction and Static Friction
• Net Force

### SOURCES:

• Physics: Principals & Problems by Paul W. Zitzewitz and James T. Murphy

Credits:

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