Forces: Weight, Spring, and Friction

• Forces can be identified by their effect on objects.
• A force can accelerate an object.
• A force can deform an object.
• The symbol for force is $F$.
• The unit of force is $[F] = 1 \text{ N (Newton)}$.

Types of Forces

• Weight force ($F_g$) indicates how strongly an object of mass $m$ is attracted by the Earth.
• Weight force always acts towards the center of the Earth.
• $F_g = m \cdot g$
• $g = 9.81 \frac{\text{m}}{\text{s}^2} \approx 10 \frac{\text{m}}{\text{s}^2}$ is the local gravitational acceleration.
• Spring force ($F_{\text{Feder}}$) is the force with which a spring opposes its displacement ($s$).
• $F_{\text{Feder}} = D \cdot s$
• $D$ is the spring constant, indicating the strength of the spring.
• Friction force ($F_R$) arises when two bodies are in contact and move or want to move against each other.
• Friction force always acts against the direction of motion.
• Static friction ($F_{R, \text{Haft}}$) is present until breakaway, and it's calculated as: $F_{R, \text{Haft}} = \mu_{\text{Haft}} \cdot F_N$
• Kinetic friction ($F_{R, \text{Gleit}}$) occurs during motion, and its formula is: $F_{R, \text{Gleit}} = \mu_{\text{Gleit}} \cdot F_N$
• $F_N$ is the normal force, which acts perpendicularly to the surface.
• $\mu$ is the coefficient of friction, dependent on the materials involved.
• Downhill force ($F_{\text{Hang}}$) is the force that pulls an object down on an inclined plane.
• $F_{\text{Hang}} = F_g \cdot \sin(\alpha)$
• $\alpha$ is the angle of the inclined plane.