Lesson 8

Chapter 2 Forces
Section 3 Driving forces and resisting forces
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Chapter 2 Forces
Section 3 Driving forces and resisting forces

Slide 1 - Diapositive

Chapter 2 Forces
Section 3 Driving forces and resisting forces
This Lesson
  • Double helical springs
  • Newtons first law
  • Air resistance
  • Practice exercises

Slide 2 - Diapositive

Lesson 8

Slide 3 - Diapositive

Force and extension
C=xF
C: Spring constant (in N/m)
F: Force (in N)
x: Extension (in m)

Slide 4 - Diapositive

Slide 5 - Vidéo

Newtons first law
If the resultant force of all the forces is zero (0N), the object is either stationary or it moves along a straight line at a constant speed

Slide 6 - Diapositive

Driving forces

Slide 7 - Diapositive

Resisting forces
Friction
Air resistance
Rolling resistance

Slide 8 - Diapositive

Air resistance
Fr,a=21CdρAv2

Slide 9 - Diapositive

Air resistance
Fr,a=21CdρAv2
  • Fr,a: Force, resistance, air resistance (n)
  • C: resistance coefficient (no unit)
  • ρ: The density of air (or whatever medium the object is traveling through) (kg/m3)
  • A: area of the object (m2)
  • v: the speed of object (m/s)

Slide 10 - Diapositive

Practice exercise
A skydiver is falling from the sky at terminal velocity of 60 m/s. This mean the forces acting on him are balanced. His weight is 735 N (downwards force). This force is balanced by the upwards force of air resistance. He has a frontal area of 0.33 m2. The density of air is 1.207 kg/m3. Calculate his drag coeficient (Cd). 

Fr,a=21CdρAv2

Slide 11 - Diapositive

Slide 12 - Diapositive

Slide 13 - Diapositive