All 10 short questions of 9th Class Physics Chapter 6, Mechanical Properties of Matter, with exam-ready answers in the book's words. Punjab Board new syllabus.
Exam-ready answers. Learn the meaning, then write them in your own words.
An elephant's weight is very large. Spread over large flat feet, the pressure on the ground (and on its leg bones) is P = F ÷ A, which stays small. With small feet the pressure would be too much for its bones and it would sink into soft ground.
A small hoof gives a large pressure on the ground for the same weight (P = F ÷ A). The hooves dig into the ground and grip it, so the deer can push off hard and run fast without slipping.
The foot touches the pebbles only at a few small points, so the contact area is small. The same body weight then gives a very large pressure (P = F ÷ A) at those points, which hurts.
Pressure applied at one point of an enclosed fluid is transmitted equally, without loss, to all parts of the fluid.
Applications: hydraulic press, car lift at service stations, hydraulic brakes of vehicles.
The property of a solid by which it regains its original size and shape when the deforming force is removed, for example a rubber band or a spring.
Within the elastic limit, the extension of a spring is directly proportional to the applied force: F = kx.
No. Beyond the elastic limit the deformation becomes permanent: the object does not return to its original shape when the force is removed, and F is no longer proportional to x.
| Force | Pressure |
|---|---|
| A push or pull that changes, or tends to change, the motion or shape of a body | Force acting normally per unit area |
| Vector | Scalar |
| Unit: newton (N) | Unit: pascal (Pa = N m⁻²) |
| F = ma | P = F ÷ A |
Liquid pressure is directly proportional to the depth: P = ρgh. Twice as deep means twice the pressure due to the liquid.
Atmospheric pressure pushing on the mercury in the dish holds up a column of mercury in the tube. Points at the same level in the mercury have the same pressure, so the pressure of the column, ρgh, equals atmospheric pressure. The height h of the column is therefore a measure of atmospheric pressure (about 760 mm at sea level).
Pascal's law. Pressing the brake pedal pushes the piston of the master cylinder and raises the pressure in the brake oil. This pressure is passed on equally to the larger pistons in the wheel cylinders, which push the brake pads against the wheels with a large force.
