3. What is space junk? Give two examples and describe why these materials pose hazards to
an astronaut or spacecraft.

disused satellites and other man-made debris in orbit around the earth.

"windows on the space shuttle are replaced regularly because of chipping caused by collisions with small pieces of space junk", Space debris is defunct artificial objects in space—principally in Earth orbit—which no longer serve a useful function

Explanation:

Human activities leave too many dead satellites and fragments of machinery discarded in Earth orbit

Explanation:

Example of space junks

2,000 active satellites in Earth's orbit

One in 10,000: risk of collision that will require debris avoidance manoeuvres

Disadvantage

Collision : might hit other major satellite in space

Junks in 'graveyard orbit' coming back to haunt

Space junk can hang around for centuries

water   molecules stay close to each other through cohesion, the collective action of hydrogen bonds between water molecules. cohesion plants draw water upwards from the root through the stem's transport tubes (xylem) to the leaf. this transport occurs even in large trees and against gravity. transpiration, evaporation of water from plant leaves, creates a tension on water molecules being pulled up from the stem and roots.

water also has high (the attraction of one substance to another) properties because of its polar nature. adhesion of water molecules to plant cell walls counteract gravity while water is transported from roots to leaves.

water exhibits a very high surface tension when compared to other liquids. surface tension is a property of a liquid that holds the surface together and allows it to resist an external force. by capillary action, the water forms concave menisci inside the pores. the high surface tension of water pulls the concavity outwards, generating enough force to lift water from the roots to the leaves of plants.

thus, cohesion, along with adhesion and surface tension creates a capillary action that keeps water molecules interacting and moving through the plants out to the leaf cells.

therefore, option d) is the correct answer.

explanation: