Yr 12 - Forces Flashcards
Tension
A pulling force caused by 2 or more forces acting on an object in opposite directions.
Compression
The reduction in volume of an object when a compressive force is exerted on it.
Friction
A resistive force on an object that is caused by two surfaces in contact.
- Friction acts in opposite direction to motion
Fluid
A substance that can flow.
- Any gas or liquid
Lift
A force caused by the flow of fluid around an object which acts perpendicular to the fluid flow.
Normal contact force
A reaction force exerted by a surface on an object.
- Always at 90 degrees (perpendicular) to the surface
Upthrust
Acts on object partially/fully submerged in fluids. The surrounding fluid pushes upwards on the object
Lift Vs Upthrust
- Lift created by flow of fluid around an objects surfaces
- Upthrust created by the displacement of a fluid
What is a Newton
Force required to accelerate a mass of 1 Kg by 1ms^-2
- Kgms^-2
Thrust
A force from an engine that is usually propulsive
Free Body Diagrams
Simple representations of multiple forces acting on a single object
Drag, speed and area
- Drag proportional to Area
- Drag proportional to Speed^2
Terminal Velocity
Maximum velocity a falling object can travel when resistive force = weight
Viscosity
A measure of a fluids resistance to flowing
- Higher = Honey
- Lower = Water
Drag
A frictional force opposing motion of an object moving through a fluid.
- Drag Proportional to Velocity^2 OR Speed^2
- Drag proportional to area
Uniform gravitational field
A region of space in which objects experience the same gravitational field strength
Centre of gravity
An imaginary point where the entire weight of an object may be considered to act
Equilibrium
Net force and net moment acting on a body is zero
Centre of Mass
A point where externally applied forces produce straight-line motion but no rotation
Principle of Moments
Sum of anti-clockwise moments = Sum of clockwise moments
- Object in equilibrium therefore no rotation
Couple
A pair of equal parallel forces acting in opposite directions from equal distances about a pivot
Torque of a couple
Force multiplied by the perpendicular distance between the forces
Archimedes Principle
The upthrust exerted on a body partially or fully submerged immersed in fluid is equal to the weight of the fluid that body displaces.
- Upthrust force = Weight of Displaced Fluid
What creates upthrust
Greater pressure at bottom of object compared to the top.
3 Things that affect Upthrust
Weight -
Weight of fluid displaced = Upthrust
Volume -
Volume of displaced fluid ∝ upthrust
Fluid Density -
Fluid Density ∝ Upthrust
