Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Friction is a contact force that occurs when two surfaces slide, or attempt to slide, across each other.
Friction always acts in the opposite direction to the direction of motion. If an object moves to the right, friction acts to the left.
The strength of friction depends on the types of surfaces; rough surfaces (like sandpaper) create more friction than smooth surfaces (like ice).
Friction can be useful, such as providing grip for shoes to walk or tires to brake, but it can also be a disadvantage by causing wear and tear and generating energy.
Air resistance and water resistance are types of friction called 'drag' that act on objects moving through gases or liquids.
Lubrication involves using substances like oil or grease to reduce friction between surfaces by creating a thin layer that separates them.
Forces, including friction, are measured in Newtons () using a device called a force meter or spring balance.
📐Formulae
💡Examples
Problem 1:
A student pulls a box across a wooden floor. A force meter shows that it takes of force to keep the box moving at a steady speed. What is the value of the friction force?
Solution:
Explanation:
When an object moves at a steady speed, the forces are balanced. This means the applied pulling force is equal to the opposing force of friction: .
Problem 2:
Why does a skydived use a parachute to slow down their fall?
Solution:
The parachute increases the surface area to maximize air resistance ().
Explanation:
Air resistance is a form of friction. By increasing the surface area, the parachute catches more air particles, increasing the upward force of to oppose the downward force of gravity ().
Problem 3:
If a surface is covered in oil, will the force required to move a block across it increase or decrease?
Solution:
The force required will decrease.
Explanation:
Oil acts as a lubricant. It fills the microscopic gaps in the surfaces, reducing the contact between them and lowering the .