# force what is force? –push or pull it’s what causes “things” to accelerate 1000 kg

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• ForceWhat is force?Push or PullIts what causes things to accelerate1000 kg

• Balanced v. Unbalanced ForcesIf all forces are balanced there is no acceleration in any direction. (Either Zero Motion or Constant Velocity)

If one force is greater than the opposing force we get acceleration in a direction.

• Balanced Forces (Balanced Forces = No Acceleration) 5 N5 NEqual PushingObjectNotice that all the forces are equally pointed in the opposite direction. Hence they balance each other or cancel each other.Forces may cancel each other and produce No Acceleration!

• Gravity pulls down on you

The ground pushes back up

THIS KEEPS YOU WHERE YOU ARE!If these football players push on each other equally as hard,will either one move?Gravity pulls downGround pushes upBalanced Forces (Balanced Forces = No Acceleration)

• 5 N5 N5 N5 NEqual PushingEqual PullingForces may cancel each other and produce No Acceleration!Balanced Forces (Balanced Forces = No Acceleration)

• Unbalanced ForcesCauses AccelerationAdding ForcesSubtracting Forces

• Adding ForcesTwo forces can add together to produce a larger net force than either original force.Positive Acceleration occurs (Speed up)5 N5 N= 10 N

• Unbalanced ForcesCauses AccelerationAdding Forces5 NObject5 NNotice that all the forces are pointed in the same direction. Hence they add together.

• Subtracting ForcesTwo forces can subtract to produce a net force in the direction of the larger force.Negative Acceleration occurs (Slow Down) 10 N5 N= 5 N

• Unbalanced ForcesCauses AccelerationSubtracting Forces5 N5 NObject5 NNotice that all the forces are unequal and pointed in the opposite direction. Hence they are unbalanced and in opposition to each other or one partially cancels the other.

• Balanced Forces10N10N10N10N

BalancedPushi.e. Pushing a CarNo AccelerationBalancedPulli.e. Tug-o-warNo Acceleration

• Un-Balanced Forces10N10N10N10N10N

• Balance between Gravity and FrictionThe skydiver is colliding with themolecules of gas in the air! Which slows down the fall of the skydiver!Q: If the friction of the air and the pull of gravity were in perfect balance, what would the skydiver be doing?A: The skydiver would be going a constant velocity (moving with no acceleration) down towards the ground until it hit the ground.

• How it worksNotice that as the skydiver leaves the plane, the force of gravity accelerates him faster towards the earth; however, the moment he jumps out of the plane, another force begins to oppose gravity Air Resistance, (Friction).

This friction with the air begins to slow down his rate of acceleration. Meaning, hes still speeding up, just not as fast.

Once the force of air friction equals the force of gravity, the skydiver steadily descends towards earth at a constant velocity.Gravity0 m/s30 m/sAir ResistanceConstant VelocitySpeed: 0 m/s10 m/s20 m/s25 m/s28 m/sAcceleratingConstant VelocityAccelerating

• Forces may cancel each other and produce No Acceleration!Balanced Forces (Balanced Forces = No Acceleration) 5 N5 NEqual PushingObjectNotice that all the forces are equally pointed in the opposite direction. Hence they balance each other or cancel each other.Wait a minute. This object was moving.Thats Right. As you may have noticed, although I may have balanced forces, I might still be moving.

Notice that when the forces are balanced, the object might still be moving, but the objects are not accelerating, instead they have a constant velocity. Hence, once in motion its always in motion unless acted upon by what? Another Force. Equal Pulling

• Constant Velocity12345In other words, you still need to use the gas peddle to balance out all the force of friction to keep you going at a constant speed.Time [Sec]Distance [m]0 1 2 3 4 5 6 5 N5 N

• AccelerationTo get an object to move faster, create an unbalanced force!1210 N5 N

• ForceSpeed = Distance divided by timeS= D/TWhat is the speed of a rocket traveling at 4,000 miles in 1.5 hours?

2,667 miles/hr

• The Law of Conservation of EnergyEnergy cannot be __________ or ____________; it may be transformed from one form into another, but the total amount of energy _________ changes.

createddestroyednever

• the ability to do work The combination of energy and matter make up the universe: Matter is substance, and energy is the ____________ of substance.

What is energy? mover

• Energy is natures way of keeping score. We sense energy only when it changes,either a transformation from one form of energy to another, or a transfer of energy from one point to another.

• How is all energy divided? All Energy

• Potential Kineticenergy of _________or energy in ______________. Water behind a damHammer over headFood on the plateenergy of ________, the form capable of doing work Flowing waterA falling hammerFood being converted into usable energy in the cell.positionstoragemotion

• PE = mgh

____ = mass (kg) ____ = height (m)____ = accel due to gravity(9.8 m/s2)

mhg

• What is Gravitational Potential Energy?Potential energy due to an objects position

P.E. = ________x ________ x _____________Dont look down, Rover!Good boy!massheightgravity

• What is Potential Energy?Energy that is stored and waiting to be used later

• What is Elastic Potential Energy?Potential energy due compression or expansion of an elastic object.Notice the ball compressingand expanding

• What is Chemical Potential Energy?Potential energy stored within the chemical bonds of an object

• What is Kinetic Energy?Energy an object has due to its motionK.E. = .5(mass x speed2)

• KE = 1/2 m v2 4 kg bowling ball at 10 m/s = .5 (4kg) (10m/s)2 = 200 J .25 kg baseball at 50 m/s = .5 (.25kg) (50 m/s)2 = 312 J

• Courtesy Jerry Ohlingers Movie Material StoreWork is done when a force is exerted over a distance.

• Workis equal to the force that is exerted multiplied by the distance over which it is exerted.W = _______The unit of work combines the unit of force (N) with the unit of distance (m) Newton-meter (N-m) aka ________.

F x dJoule

• You carry a 20 kg suitcase upstairs, a distance of 4m. How much work did you do? W = F x d F = ma = (20 kg) (10m/s2) = 200 N W = F x d = (200 N) (4m) = 800 J

• 6 fundamental forms of energymechanical energyThermal (heat) energyelectromagnetic energyelectrical energynuclear energychemical energy

• What is the source of our energy? The source of practically all our energy is the _______.SUN

• What is Mechanical Energy? Energy due to a objects _________ (kinetic) or __________ (potential).

The bowling ball has mechanical energy.

When the ball strikes the pins, mechanical energy is transferred to the pins!motionposition

• Examples of Mechanical Energy

• What is ElectromagneticEnergy? _________________

Includes energy from gamma rays, xrays, ultraviolet rays, visible light, infrared rays, microwave and radio bandsLight energy

• What is Electrical Energy? Energy caused by the movement of _____________

Easily transported through power lines and converted into other forms of energyelectrons

• What is Chemical Energy? Energy that is available for release from _____________________.

The chemical bonds in a matchstick store energy that is transformed into thermal energy when the match is struck.Chemical reactions

• Examples of Chemical Energy

• What is Thermal Energy? Heat energy

The heat energy of an object determines how active its atoms are.

A hot object is one whose atoms and molecules are excited and show rapid movement.

A cooler object's molecules and atoms will show less movement.

• QUIZ TIME!What type of energy cooks food in a microwave oven?ELECTROMAGNETIC ENERGY

What type of energy is the spinning plate inside of a microwave oven?MECHANICAL ENERGY

• QUIZ TIME!Electrical energy is transported to your house through power lines.

When you plug an electric fan to a power outlet, electrical energy is transform into what type of energy?

MECHANICAL ENERGY

• QUIZ TIME!

What energy transformation occurs when an electric lamp is turned on?

ELECTRICAL ENERGYELECTROMAGNETIC ENERGY

• What types of energy are shown below?Mechanical and Thermal Energy(Dont forget friction)

• What type of energy is shown below?Chemical Energy

• What types of energy are shown below?Electrical, Mechanical andElectromagnetic Energy

• What type of energy is shown below?Chemical Energy (yummy)

• What type of energy is shown below?Thermal Energy

• What types of energy are shown below?Mechanical, Electromagnetic, Electrical, Chemical and Thermal Energy

• The Law of Conservation of EnergyEnergy cannot be created or destroyed; it may be transformed from one form into another, but the total amount of energy never changes.

*

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