Aerodynamics: Lift, Drag and Thrust
The forces that act on a moving vehicle or aircraft: thrust, drag, lift and weight, how they work in opposing pairs, and how balanced and unbalanced forces change the motion.
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Forces on a plane
When a plane flies, four forces act on it at once. The engine drives it forward, the air pushes back, the wings hold it up, and gravity pulls it down. Understanding how these forces balance is the heart of aerodynamics. This module looks at each force and at how they change the motion of a vehicle.
Force words
Learn these four forces before you study how they act.
Forces in opposing pairs
The four forces work as two opposing pairs, one horizontal and one vertical.
Think in opposing pairs
A strong answer treats the forces as two opposing pairs: thrust against drag, and lift against weight. Work out the resultant force in each pair by taking the smaller force from the larger. If a pair is balanced the motion stays steady; if it is unbalanced the object speeds up, slows down, rises or falls.
Match the term
- streamlining
- aerofoil
- resultant force
- balanced forces
- a smooth shape that reduces air resistance
- a wing shape that helps create lift
- the overall force left after opposing forces combine
- forces that cancel out, giving a steady motion
Match the direction
- thrust
- drag
- lift
- weight
- acts forwards, in the direction of travel
- acts backwards, against the motion
- acts upwards
- acts downwards, toward the ground
Steady and level
A plane flies at a steady speed in a straight, level line. What must be true of the forces?
- Thrust balances drag and lift balances weight.
- Thrust is much greater than drag.
- There is no drag at all.
- Weight is greater than lift.
Cutting the drag
Select the TWO things that reduce the drag on a vehicle.
- Giving it a smooth, streamlined shape.
- Giving it a smooth, pointed front.
- Making it large and flat at the front.
- Giving it a rough, bumpy surface.
Getting off the ground
Put the stages of a plane taking off in order, earliest first.
- The engines increase the thrust
- The plane speeds up along the runway
- Air flows faster over the wings and lift grows
- Lift beats weight and the plane rises
Complete the facts
On a plane, _____ pushes it forwards while _____ pushes back against it. The _____ from the wings must beat the plane _____ for it to climb. Making a car more _____ lowers its air resistance.
Work out the resultant
A plane engine produces a thrust of 5000 newtons. The drag on the plane is 3000 newtons. The resultant forward force is the thrust minus the drag. What is it in newtons?
Find the vertical forces
Tap the TWO forces that act straight up or straight down on a plane.
- lift
- weight
- thrust
- drag
What is happening?
Read each situation and choose what is going on.
- A cyclist crouches low over the handlebars to go faster
- A plane wing is curved on top so air moves faster over it
- A rocket engine fires and pushes the rocket upwards
Explain the forces
Explain the four forces that act on an aircraft in flight. For each force say which direction it acts and what it does, and explain what happens when the forces become unbalanced.
- Name the four forces on an aircraft
- Say which direction each one acts
- Explain what happens when the forces become unbalanced