Energy
l Ability to do work
l To cause something to change move or directions
l Energy cannot be created or destroyed, but transferred from one form to another.
l Energy quality is lost due to friction / force/ heat.
-From high quality energy to low quality energy.
Newton’s 1st Law of Motion
l Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.
l Inertia – Forces that resist to motion
Inertia
l An object in motion tends to stay in motion unless acted upon by a force.
l An object at rest tends to stay at rest unless acted on by a force.
l Friction - The resistance encountered when one body is moved in contact with another.
The four types of friction
l Static friction- friction between two surfaces that are not moving past each other.
l Sliding friction- the force that opposes the motion of two surfaces sliding past each other.
l Rolling friction- the friction between a rolling object and the surface it rolls on.
l Fluid friction- when an object is moving in liquid or gas.
Friction
•Slows an object down until it stops
•Produces heat
•Wears object down
n Aerodynamic: Designed or arranged to offer the least resistant to fluid flow.
n Hydrodynamic: A shape designed to move efficiently through the water.
3rd Law of Motion
l For every action there is an equal and opposite reaction.
Newton’s 2nd Law
l The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma.
The net force on an object is equal to the mass of the object multiplied by its acceleration.
First law of energy (thermodynamics)
l All energy is either kinetic or potential.
Potential Energy: (PE) The energy stored by an object as a result of its position
l Potential Energy is the energy of position. Objects that are elevated have a high potential energy.
l Kinetic Energy is the energy of motion
PE = MGH
l PE = Energy (in Joules)
l m = mass (in kilograms)
l g = gravitational acceleration of the earth (9.8 m/sec2)
l h = height above earth's surface (in meters)
Kinetic Energy
l The energy that matter has because of its motion and mass.
l where m = mass of object
l v = speed of object
l KE = Energy in Joules
• Don’t forget your order of operations.
• PEMDAS
• For KE, you must do exponents (E) before multiplying (M). So square the velocity first, and multiply by half of the mass.
Kinetic energy
l The energy that matter has because of its motion and mass.
l The flow of electrons or charged particles called electrical energy are all examples of kinetic energy.
l Amount of energy depends on both its mass and its velocity (speed).
l Mechanical Energy (ME) – Energy due to position and motion; sum of potential and kinetic energies. Includes heat and friction.
l Just add Potential Energy + Kinetic Energy.
n Hydropower – Potential to Kinetic energy
l Speed = Distance over time
l 80 km / 2 hrs = 40 km / hr
l 80 miles / 2 hrs = 40 mph
n Velocity = Speed (distance / time) and direction.
n Acceleration = The rate of change in velocity.
n Acceleration = The final velocity – the starting velocity, divided by time.
n Deceleration – To slow velocity
n Momentum: A measure of the motion of a body equal to the product of its mass and velocity.
n Momentum = Mass times velocity
l Amount of Work (w) done depends on two things:
The amount of Force (F) exerted.
The Distance (d) over which the Force is applied.
n Equation for Work - w = F x d
l Machines help us to do work!
l One Joule = N over a meter (N-m)
n Catapults - By the law of conservation of energy, the stored potential energy (U) is transferred into rotational kinetic energy (K), with some loss due to friction. U = K
n Trajectory – The path of flying object: the path that a projectile makes through space under the action of given forces such as thrust, wind, and gravity.
l Force: Is a PUSH or a PULL, that causes a change in the motion or shape of an object
l Gravity, Electricity, Magnetism, and Friction
l F = w x d.
l W = F x d
Machines…
l Transfer force from one place to another.
l Change direction of a force.
l Increase the magnitude of a force.
l Increase the distance or speed of a force.
l Force is a quantity which is measured using the standard metric unit known as the newton
l One newton is the amount of force required to give a 1-kg mass an acceleration of 1 m/s/s.
Quick Cheat Sheet
l Potential Energy (PE) = mass kg * gravity (9.8) * height (Answer is in Joules)
l Kinetic Energy (KE) = ½ mass kg * Velocity squared (velocity * Velocity) (Answer is in Joules)
l Square velocity first because it an exponent (PEMDAS)
l Mechanical Energy (ME) = Kinetic Energy + Potential Energy (Answer is in Joules)
l Speed – A Measure of motion, = Distance divided by time (Answer in meters per second m/s)
l Velocity – Rate of which an object changes its position. = Distance divided by time and direction. (Answer in meters per second and direction such North, East, South, West, or Northwest etc.)
l Acceleration – Change in velocity over time. Final Velocity minus the starting velocity divided by time. (Answer is in meters / sec/ and direction North, etc.
l Deceleration – Same as acceleration but the number will be negative.
l Mass – Amount of matter in an object. On earth, weight and mass are the same. (Metric unit is the gram)
l Force = (F=MA) F = Mass (Weight on earth) * Acceleration (Answer is in newtons (m/s/s)
l Work – Force * Distance the force was applied (Answer is in newtons)
New Area of Focus: Simple machines
l Types of machines that do work with one movement.
Pulley
l Uses grooved wheels and a rope to raise, lower or move a load.
Three types of pulleys
l A pulley makes work seem easier
l Changes the direction of motion to work with gravity. Instead of lifting up, you can pull down.
l Uses your body weight against the resistance.
l The more pulleys that are used, the more the MA (Mechanical Advantage).
l MA = The number of ropes that support the pulley. The end of the rope doesn’t count.
The three types of Pulleys
Fixed pulley
No Mechanical Advantage
Movable Pulley
Combined Pulley / Block and tackle
Lever
l A stiff bar that rests on a support called a fulcrum which lifts or moves loads
l MA = length of effort arm ÷ length of resistance arm.
The 3 types of levers
Third Class Lever.
l Has Mechanical Disadvantage.
l Requires more force to lift the load.
n Wedge: An object with at least one slanting side ending in a sharp edge, which cuts material apart.
n The mechanical advantage of a wedge can be found by dividing the length of the slope (S) by the thickness (T) of the big end.
n Wheel and Axle: A wheel with a rod, called an axle, through its center lifts or moves a load.
n The mechanical advantage of a wheel and axle is the ratio of the radius of the wheel divided by the radius of the axle.
n Radius: A straight line from a circles center to its perimeter.
Divide 5 by 1
n An Inclined plane: A slanting surface connecting a lower level to a higher level
n MA for an inclined plane is the length of the slope divided by the height (Rise).
n Screw: An inclined plane wrapped around a pole which holds things together or lifts materials.
n The mechanical advantage of a screw can be found by dividing the circumference of the screw by the pitch of the screw.
n The circumference of a circle is the distance around the circle. It is the circle's perimeter. The formula for circumference is:
n Circumference = π times Diameter
n C = πd
n Where π = 3.14
n Compound machines: Two or more simple machines working together.
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