Cards In This Deck

• $$\begin{gathered} \text{True or False?} \\ \text{An object moving with constant velocity has no friction acting on it.} \end{gathered}$$
  $$\begin{gathered} \text{❌ False} \\ \text{✅ Correct Answer: Friction may still act, but the resultant force is zero.} \\ \text{Constant velocity means }a=0\text{, so Forward Force = Resistive Force (Friction).} \end{gathered}$$
• $\text{What is the formula for the maximum (limiting) friction force?}$
  $$\begin{gathered} F_{max}= \\ \mu R \\ \text{Where:} \\ \mu \text{ = coefficient of friction} \\ R\text{ = normal reaction force} \end{gathered}$$
• $$\begin{gathered} \text{True or False?} \\ \text{The coefficient of friction } \\ \mu \text{ can be measured in Newtons.} \end{gathered}$$
  $$\begin{gathered} \text{❌ False} \\ \text{✅ Correct Answer: } \\ \mu \text{ is a dimensionless scalar (it has no units).} \\ \text{It is a ratio of two forces: } \\ \mu =\frac{F}{R}\text{.} \end{gathered}$$
• $$\begin{gathered} \text{True or False?} \\ \text{The friction force }F\text{ acting on a rough surface is always calculated using }F= \\ \mu R\text{.} \end{gathered}$$
  $$\begin{gathered} \text{❌ False} \\ \text{✅ Correct Answer: }F= \\ \mu R\text{ only applies when the object is moving or in limiting equilibrium (on the point of moving).} \\ \text{If the object is stationary and not on the point of slipping, }F< \\ \mu R\text{ (Friction equals the applied force).} \end{gathered}$$
• $\text{In a dynamics problem involving a rough inclined plane, how do you determine the direction of the friction force?}$
  $\text{Friction always acts in the direction opposite to the motion (if moving) or opposite to the tendency of motion (if stationary).}$
• $$\begin{gathered} \text{An object moves to the right on a rough surface. } \\ \text{What is the direction of the Friction force?} \end{gathered}$$
  $\text{To the left.}$
• $\text{A particle is in equilibrium on a rough inclined plane. You need to determine the direction of the friction force. How do you decide?}$
  $$\begin{gathered} \text{Friction acts in the direction opposite to the potential motion.} \\ \text{Ask yourself: "If the surface were smooth, which way would the particle move?" Friction points the other way.} \end{gathered}$$
• $$\begin{gathered} \text{True or False?} \\ \text{If }{F}_{max}=20N\text{ and the applied force trying to move the object is only }10N\text{, then the friction force is }20N\text{.} \end{gathered}$$
  $$\begin{gathered} \text{❌ False} \\ \text{✅ Correct Answer: The friction force is }10N\text{.} \\ \text{In non-limiting equilibrium (}F< \\ \mu R\text{), friction is ’lazy’—it only exerts exactly enough force to oppose the motion and maintain equilibrium, up to the maximum limit.} \end{gathered}$$
• $\text{What is the mathematical consequence of modelling a pulley or surface as smooth?}$
  $\text{There is no friction.}$