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.”