📚 Topic Summary
Friction is a force that opposes motion between surfaces in contact. In AP Physics 1, we typically deal with two types of friction: static friction and kinetic friction. Static friction ($f_s$) prevents an object from starting to move, and its maximum value is given by $f_{s,max} = \mu_s N$, where $\mu_s$ is the coefficient of static friction and $N$ is the normal force. Kinetic friction ($f_k$) acts on an object already in motion, and its value is given by $f_k = \mu_k N$, where $\mu_k$ is the coefficient of kinetic friction. It's important to remember that $\mu_s$ is usually greater than $\mu_k$, meaning it takes more force to start an object moving than to keep it moving.
When solving friction problems, always start by drawing a free-body diagram to identify all the forces acting on the object. Then, apply Newton's second law ($\Sigma F = ma$) to find the net force and acceleration. Pay close attention to whether the object is at rest or in motion to determine whether to use static or kinetic friction.
🧠 Part A: Vocabulary
Match the following terms with their definitions:
| Term |
Definition |
| 1. Static Friction |
A. The force that opposes the motion of an object already in motion. |
| 2. Kinetic Friction |
B. The force exerted by a surface that supports the weight of an object. |
| 3. Coefficient of Static Friction |
C. The ratio of the force of static friction to the normal force. |
| 4. Coefficient of Kinetic Friction |
D. The force that opposes the initiation of motion. |
| 5. Normal Force |
E. The ratio of the force of kinetic friction to the normal force. |
Match the numbers to the letters.
✍️ Part B: Fill in the Blanks
Friction is a force that opposes ______. There are two main types: ______ friction and ______ friction. The maximum force of static friction is proportional to the ______ force and the coefficient of ______ friction. Once an object is moving, the force of ______ friction remains relatively constant.
🤔 Part C: Critical Thinking
Explain, using examples, how the angle of a ramp affects the force of friction acting on a block placed on the ramp.