6.1 Define the following terms: 6.1.1 Stress 6.1.2 Strain 6.2 A steel bar experiences a stress of 250 MPa - NSC Technical Sciences - Question 6 - 2020 - Paper 1

Strain is a dimensionless measure of deformation representing the displacement between particles in a material body. It can be calculated as:

To calculate the strain on the bar, we first use the relationship between stress, strain, and modulus of elasticity, denoted as E:

Converting units, we have:

To find the force exerted on the bar, we first calculate the cross-sectional area A:

Now we can calculate the force using the stress formula:

The viscosity of a fluid generally decreases with an increase in temperature. This is because higher temperatures provide more energy to the fluid molecules, allowing them to overcome intermolecular forces more easily, resulting in reduced friction and lower viscosity.

A perfectly plastic body is a material that deforms continuously and permanently under the application of a stress without any increase in stress during the process. Once the yield point is reached, the material does not return to its original shape.

Two examples of perfectly plastic bodies are:

1. Clay
2. Putty

Pascal's law states that in a confined fluid at rest, any change in pressure applied at any point in the fluid is transmitted undiminished throughout the fluid in all directions.

To calculate the required force on the second piston, we use Pascal's principle:

Where:

• $F_1 = 20000 ext{ N}$ (force due to vehicle)
• $A_1 = 0.8 ext{ m}^2$ (area of the vehicle's piston)
• $A_2 = 0.05 ext{ m}^2$ (area of the applied force)

Rearranging to find $F_2$ gives:

The thrust of a liquid refers to the force exerted by the liquid on an object immersed in it, which acts perpendicular to the surface of the object. This force is a consequence of the pressure exerted by the liquid at the object's surface.