Question

Bridges and sidewalks have regularly spaced cracks built into them because when it is hot, the cement _______.

1) increases its volume and needs space to grow into
2) decreases its volume and therefore needs to grow out of it
3) increases its density and therefore gains more mass
4) decreases its density and therefore loses mass

Answer 1

Bridges and sidewalks have regularly spaced cracks, known as expansion joints, to accommodate the increase in volume due to thermal expansion when temperatures rise. These structures need space to expand to prevent damage, and engineers design these features to handle the expected changes.

Step-by-step explanation:

The student's question revolves around why bridges and sidewalks have regularly spaced cracks built into them. The correct answer is that when it is hot, the cement increases its volume and needs space to grow into. This is because the thermal expansion is the change in size or volume of a given mass with temperature increase. As temperatures rise, the kinetic energy of the atoms in the material increases, leading to expansion.

Expansion joints are specifically designed features that allow bridges, sidewalks, and other structures to safely expand and contract without causing damage. Similar principles apply to railroad tracks, power lines, and even dental fillings, all of which must accommodate changes in temperature to avoid structural damage or discomfort. Thermal stress can cause serious issues like buckling of roadways, sagging of power lines, and cracking of materials if not properly managed.

It is essential for engineers to account for these natural phenomena in their designs, using materials with matching expansion coefficients or including features like expansion joints to handle the thermal stress effectively.

Answer 2

Bridges and sidewalks incorporate cracks or expansion joints to cope with thermal expansion, which is the cement's increase in volume due to rising temperatures. These joints allow structures to expand and retract without causing damage or buckling.

Step-by-step explanation:

Bridges and sidewalks have regularly spaced cracks built into them because when it is hot, the cement increases its volume and needs space to grow into. This phenomenon is known as thermal expansion, which is the change in size or volume of a given mass with temperature. The underlying cause of thermal expansion is an increase in the kinetic energy of the individual atoms as the temperature rises. To account for this, gaps or expansion joints are deliberately left in the construction of bridges and sidewalks to allow them to freely expand and contract with temperature changes.

Railroad tracks, roadways, power lines, and even biological systems can be affected by thermal stress. For example, railroad tracks and roadways can buckle on hot days if they lack sufficient expansion joints, and power lines may sag more in summer and snap in cold weather if there is not enough slack. In engineering materials, matching coefficients of thermal expansion is crucial to prevent excess stress which may lead to structural failures or cracks in materials.