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Forces, Planes and propellers

Topic 1: Forces A force is any influence that can change the trajectory, speed or shape of a body. Effects produced by a force –Change in state of motion of a body –Distortion of a body

Forces Forces (measured in Newtons) are qualified by both direction and magnitude (represented by a vector)

Forces

Forces can –Accelerate an object Force is applied in the same direction of the motion –Decelerate an object Force is applied in the opposite direction of the motion –Modify the trajectory Force is applied on the side of the object

Forces What will be the total force? Resultant Force:

Forces What will be the resultant force? Resultant Force:

So let’s say… 2 people are each trying to push an elephant with a force of 40 N What is the resultant force? –Equilibrium of forces

Forces –Resultant Force: Forces in the same direction are added Forces in the opposite direction are subtracted –Equilibrium of forces is achieved then the resultant force on an object is zero. When the forces acting on the object are of same magnitude and in opposing direction

Forces Force (N) is any influence that can change the trajectory, speed or shape of a body. Change in state of motion of a body Distortion of a body A force is represented by a vector with both direction and magnitude

Forces If a force is applied –in the same direction as the motion of a body it will accelerate –in the opposite direction as the motion of a body it will decelerate –Perpendicularly to the direction of motion of a body it will change trajectories

Forces An equilibrium of forces is achieved when the resulting force is equal to 0 *** –Add forces in the same direction –Subtract forces in opposing direction

Types of forces Magnetic Force –Force of attraction/repulsion between two magnetic substances The FORCE

Types of Forces Electromagnetic Force –Force of attraction/repulsion between two charged objects Friction –Force that resists relative motion between two bodies in contact. Depends on surface and pressure applied

Types of Forces Gravitational Force –Always towards the center of the Earth –w = Fg = m * g Wherew = weight (N) Fg = Gravitational Force (N) g = Gravitational Constant (N/kg) m = Mass (Kg)

Calculating gravitational force What is the mass of a 70 kg astronaut on Earth? (g = 9.8) What is the mass of the same astronaut on the moon? (g=1.67) What is the weight of the same astronaut on the moon? (g=1.67)

Types of forces Magnetic Force –Force of attraction/repulsion between two magnetic substances Electromagnetic Force –Force of attraction/repulsion between two charged objects

Types of Forces Gravitational Force –Always towards the center of the Earth –w = Fg = m * g Wherew = weight (N) Fg = Gravitational Force (N) g = Gravitational Constant (N/kg) m = mass (kg)

Application of forces The challenge of flight

Forces of flight Drag –force that opposes an aircraft's motion through the air Lift –Force that directly opposes the weight of a plane (requires a fluid medium and motion) Gravity Thrust –Force that moves an airplane forward

Which forces should be larger?

How do we achieve this?

Principle behind the propeller and wings Bernoulli’s Principle: –Shows the relation between velocity, pressure and density of a fluid –“An increase in speed of the fluid results in a decrease of pressure.

Airplane wing application

Airplane Propeller application

Propeller lingo Propeller Pitch: –The distance the propeller will travel through the fluid in one rotation Propeller angle: –The angle between the blade and the plane of rotation –http://www.youtube.com/watch?v=R7hyrD9-R4A

Torque Effect

Leading edge: –Edge of the blade that “cuts” through the wind Trailling edge: –Edge of the blade that does not “cut” through the wind

Twisting of the blades: –Due to the variation in the speed of rotation of the propeller (center vs. tip) a twist is given to meet the wind –Makes sure that your propeller blades do not break apart in flight

Bernoulli’s Principle –“An increase in speed of the fluid results in a decrease of pressure.”

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