Yr 12 - Forces

Question 1

Tension

Answer 1

A pulling force caused by 2 or more forces acting on an object in opposite directions.

Question 2

Compression

Answer 2

The reduction in volume of an object when a compressive force is exerted on it.

Question 3

Friction

Answer 3

A resistive force on an object that is caused by two surfaces in contact.

• Friction acts in opposite direction to motion

Question 4

Fluid

Answer 4

A substance that can flow.

• Any gas or liquid

Question 5

Lift

Answer 5

A force caused by the flow of fluid around an object which acts perpendicular to the fluid flow.

Question 6

Normal contact force

Answer 6

A reaction force exerted by a surface on an object.

• Always at 90 degrees (perpendicular) to the surface

Question 7

Upthrust

Answer 7

Acts on object partially/fully submerged in fluids. The surrounding fluid pushes upwards on the object

Question 8

Lift Vs Upthrust

Answer 8

• Lift created by flow of fluid around an objects surfaces
• Upthrust created by the displacement of a fluid

Question 9

What is a Newton

Answer 9

Force required to accelerate a mass of 1 Kg by 1ms^-2
- Kgms^-2

Question 10

Thrust

Answer 10

A force from an engine that is usually propulsive

Question 11

Free Body Diagrams

Answer 11

Simple representations of multiple forces acting on a single object

Question 12

Drag, speed and area

Answer 12

• Drag proportional to Area
• Drag proportional to Speed^2

Question 13

Terminal Velocity

Answer 13

Maximum velocity a falling object can travel when resistive force = weight

Question 14

Viscosity

Answer 14

A measure of a fluids resistance to flowing

• Higher = Honey
• Lower = Water

Question 15

Drag

Answer 15

A frictional force opposing motion of an object moving through a fluid.

• Drag Proportional to Velocity^2 OR Speed^2
• Drag proportional to area

Question 16

Uniform gravitational field

Answer 16

A region of space in which objects experience the same gravitational field strength

Question 17

Centre of gravity

Answer 17

An imaginary point where the entire weight of an object may be considered to act

Question 18

Equilibrium

Answer 18

Net force and net moment acting on a body is zero

Question 19

Centre of Mass

Answer 19

A point where externally applied forces produce straight-line motion but no rotation

Question 20

Principle of Moments

Answer 20

Sum of anti-clockwise moments = Sum of clockwise moments

• Object in equilibrium therefore no rotation

Question 21

Couple

Answer 21

A pair of equal parallel forces acting in opposite directions from equal distances about a pivot

Question 22

Torque of a couple

Answer 22

Force multiplied by the perpendicular distance between the forces

Question 23

Archimedes Principle

Answer 23

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

Question 24

What creates upthrust

Answer 24

Greater pressure at bottom of object compared to the top.

Question 25

3 Things that affect Upthrust

Answer 25

Weight -
Weight of fluid displaced = Upthrust

Volume -
Volume of displaced fluid ∝ upthrust

Fluid Density -
Fluid Density ∝ Upthrust