Topic 15: Forces and Matter

Question 1

What is fluid?

Answer 1

A liquid or a gas

Question 2

In any fluid, at what angle do the forces due to pressure act on a given surface?

Answer 2

At right angles normal to the surface

Question 3

Why does atmospheric pressure vary with the height above the earths surface?

Answer 3

The number of air molecules decreases the higher you go, this means that the weight of air above a point decreases meaning the pressure also decreases

Question 4

What direction does pressure act in?

Answer 4

All directions

Question 5

How does pressure in fluids increase with depth?

Answer 5

As the depths increases the mass of the liquid above the point also increases, this means that the force produced by that mass also increases, since the force has increased whilst the area has remained constant the pressure will increase

Question 6

Why does pressure in fluids increase with density?

Answer 6

As density increases there are more particles in a given volume of the liquid, hence the weight of the liquid is increased, this means that the force of liquid above a certain point is larger since the force has increased, the pressure must also increases

Question 7

What equation shows the magnitude of pressure in liquids at different depths?

Answer 7

Pressure = column height x density x gravitational field strength

Question 8

Why are objects in a fluid subject to an up thrust?

Answer 8

When an object is submerged in fluid, it experiences a higher pressure below it than it does on top of it and this leads to an upwards force called up thrust

Question 9

What is the magnitude of the upthrust felt by an object?

Answer 9

Upthrust is equal to the weight of fluid displaced by the object

Question 10

How can you determine is an object will sink or float?

Answer 10

If the upthrust is greater than the weight of the object, it will float, if the weight is greater force it will sink

Question 11

Why does an object with a density more than that of water would never float?

Answer 11

Upthrust is equal to the weight of the displaced fluid, if the density of the object is high, there wouldn’t be enough volume displaced to produce an upthrust larger than the objects weight, this means that it will sink

Question 12

How many forces are required to compress, bend or stretch an object?

Answer 12

More than one

Question 13

What is the relationship between the force applied and the extension of an elastic object?

Answer 13

The extension is directly proportional to the force applied, provided that the limit of proportionality isn’t exceeds

Question 14

What is meant by an inelastic deformation?

Answer 14

A deformation which results in the object being permanently changed and the object doesn’t return to its original Sh sow when the force is removed

Question 15

What is the equation linking force, spring constant and extension?

Answer 15

Force = spring constant x extension

Question 16

What type of energy is stored in a spring when it’s stretched?

Answer 16

Elastic potential energy

Question 17

What can extension be replaced with in the equation for spring force?

Answer 17

Compression

Question 18

What is elastic and I elastic distortion?

Answer 18

Elastic distortion is a temporary change, the object reverts to its original shape once the forces are removed
Inelastic distortion leads to a permanent change in shadow, it’s irreversible

Question 19

How can you calculate the work done/stored in stretching a spring?

Answer 19

Energy = 1/2 x spring constant x extension^2

Question 20

When is there a linear relationship between force and extension?

Answer 20

When an object is forming elastically; when it hasn’t yet reached the limit of proportionality

Question 21

When is there a nonlinear relationship between force and extension?

Answer 21

When the limit of proportionality had been exceeded, and the object is undergoing plastic deformation