forces, planes and propellers. topic 1: forces a force is any influence that can change the...
TRANSCRIPT
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
• 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• Where w = 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• Where w = 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
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.”