14. Friction & Air Resistance

Success Criteria

Your learning has been successful if you can do the following:

Define acceleration and its units.
Calculate acceleration from speed and time measurements.

Vocabulary

Learn these so you can communicate this concept well.

Average speed: Calculated by the total distance travelled divided by the total time taken for the journey.
Gradient / slope: How steep a line on a graph is.
Speed: How fast an object is moving.
Velocity: Similar to speed, but also tells us the direction in which an object is moving. It includes both speed and direction of motion.

Lesson 14: Hei Mahi (Do Now)

Do Now: on Pg 43 of your SciPAD (find a space!)

Give some examples of friction from a solid, a liquid and a gas.

Lesson 4: Exit Task

Find some space on page 15 of your PESS1.2 SciPAD,
and answer the following questions:

What does each letter in CUTLASS stand for?

Friction

Friction is the force that opposes the motion of an object when it comes into contact with another object or surface.

It occurs due to irregularities in the surfaces of objects, causing resistance when they slide or move past each other.

Friction is everywhere in our everyday lives, influencing various activities and processes.

Types of Friction

There are different types of friction:

Static Friction

This type of friction occurs when two surfaces are stationary relative to each other. It prevents an object from moving when force is applied, until the force overcomes the static frictional force, initiating motion.

Kinetic / sliding Friction

Kinetic friction arises when two surfaces are in motion relative to each other. It opposes the direction of motion, acting to slow down or stop the movement.

Rolling Friction

Rolling friction is experienced when an object rolls over a surface. It is generally less than sliding friction, making it easier for objects like wheels to roll.

Fluid friction also known as fluid resistance or drag

This is a type of friction that occurs when an object moves through a fluid such as air or water. Unlike solid friction, which occurs between solid surfaces, fluid friction arises due to the interaction between the moving object and the molecules within the fluid.

Factors Affecting Friction

There are three factors that affect friction:

Surface Roughness: Rough surfaces generate greater friction than smooth surfaces due to increased contact points.
Normal Force: Friction is directly proportional to the normal force pressing the surfaces together.
Material Properties: Different materials exhibit varying levels of friction depending on their properties.

Air Resistance

Air resistance, also known as drag, is the force exerted by air molecules on objects moving through the air. It opposes the motion of the object, affecting its speed and trajectory. Air resistance becomes particularly significant at higher speeds or for objects with large surface areas.

There are several factors affecting air resistance:

Speed: Air resistance increases with the speed of the object. Faster-moving objects experience greater resistance.
Cross-sectional Area: Objects with larger surface areas experience more air resistance.
Shape: The shape of an object affects how air flows around it. Streamlined shapes encounter less resistance compared to irregular shapes.
Density of the Medium: Air resistance also depends on the density of the medium through which the object is moving. For example, objects experience less air resistance in thinner air at higher altitudes.