Forces (5) - Pt2

Question 1

What’s the limit of proportionality?

Answer 1

The point on a extension-force graph, where the extension is no longer proportional to the force

Question 2

What’s the formula to find elastic potential energy?

Answer 2

Elastic potential energy (J) = 1/2 x spring constant (N/m) x Extension (m)2
Ee = 1/2Ke2

Question 3

In elastic deformation what’s the relationship between work done and elastic potential energy stored?

Answer 3

the work done on the spring and the elastic potential energy stored are equal.

Question 4

What’s a moment?

Answer 4

A force or several forces which cause an object to rotate.

The turning effect of a force is called its moment

Question 5

What formula gives you the size of the moment?

Answer 5

Moment of a force (Nm) = Force (N) x Distance (m)-the
Perpendicular distance from the pivot to the line of action of the force
M=Fd

Question 6

Give an example of a moment? And how would you make the moment larger?

Answer 6

• The force on the spanner causes a moment on the nut (acting as a pivot)
• a larger force or a longer distance (spanner) would mean a larger moment

Question 7

What would you do (that doesn’t affect the force or distance) to get the maximum moment?

Answer 7

Push at right angles (perpendicular) to the spanner

Pushing at another angle would mean a smaller distance and so a smaller moment.

Question 8

If an object is balanced, the total clockwise moment about a pivot equals the ….

Answer 8

Anticlockwise moment

Question 9

What are simple lever and a simple gear system used for?

Answer 9

to transmit the rotational effects of forces.

Question 10

How do levers work?

Answer 10

• they increase the distance from the pivot at which the force is applied (M=Fd so less force for the same moment)
• levers make it easier to do work

Question 11

Explain how gears transmit rotational effects

Answer 11

• the teeth of the gears interlock, causing each other to turn in opposite directions
• different sized gears can Change the moment of the force
• a force transmitted to a larger gear will cause a bigger moment as the distance to the pivot is greater

Question 12

What fluids?

Answer 12

• substances that can flow (liquid/gas) because their particles move around
• these move around and collide with surfaces and other particles
• the particles have a mass and so exert a force when they collide, exerting pressure

Question 13

What’s pressure?

Answer 13

Force per unit area

Question 14

What’s the pressure of a fluid?

Answer 14

A force exerted at right angles (normal)to any surface in contact with the fluid

Question 15

How can you calculate the pressure at the surface of a fluid?

Answer 15

Pressure (Pa) = Force normal to a surface (N)/ Area if that surface (m*2)
P= F/A

Question 16

What’s density?
What’s the density of a liquid?
What’s the density of a gas?

Answer 16

• how close together the particles in a substance are
• in a liquid the density is uniform and doesn’t vary with shape or size
• the density of a gas can vary though

Question 17

Explain what the pressure in a liquid depends on?

Answer 17

• the denser a liquid the more particles in a certain place so they collide more, so it increases the pressure
• increasing the depth of a liquid increases the number of particles above the liquid the weight of these parties add to the pressure
• so pressure in a liquid depends on depth and density

Question 18

How do you find the pressure of a liquid?

Answer 18

Pressure (Pa) = height of the column of liquid (the depth)(m) x Density of the liquid (kg/m*3) x gravitational fried strength (N/kg)
P = h roh g

Question 19

Define upthrust

Answer 19

• upthrust is equal to the weight of fluid that has been displaced by the object
• a submerged object experiences a greater pressure on the bottom surface than on the top surface. This creates a resultant force upwards. This force is called the upthrust.

Question 20

What’s happening when an object floats?

Answer 20

The upthrust is equal to the objects weight

The forces are balanced so the object floats

Question 21

What’s happening when an object sinks?

Answer 21

The objects weight is more than the upthrust so the object sinks

Question 22

In terms of density explain how an object floats?

Answer 22

• An object less dense then the fluid it’s in weighs less than the equivalent volume of fluid
• this means it displaces a volume of a fluid that’s equal to its weight
• the objects weight is equal to the upthrust so it floats

Question 23

Explain in terms of density why an object sinks?

Answer 23

• An object denser than the fluid it’s in is unable to displace enough fluid to equal its weight
• This means the weight is larger than the up thrust so it sinks

Question 24

Explain how submarines use upthrust?

Answer 24

• to sink they fill large tanks with water to increase the weight of the submarine so it’s more than the upthrust
• to rise the tanks are filled with compressed air to reduce the weight so that it’s less than the upthrust

Question 25

What’s the atmosphere?

Answer 25

A layer of air that surrounds Earth. It’s thin compared to the size of earth

Question 26

What’s atmospheric pressure?

Answer 26

• created on a surface by air molecules colliding with the surface
• as the a,titube increases the atmospheric pressure decreases
• as the altitude increases, the atmosphere gets ,ses dense so there’s fewer air molecules that can collide with the surface
• there’s also fewer air molecules above the surface as the altitude increases this means the weight of air above it decreases with altitude

Question 27

What’s the difference between displacement and distance?

Answer 27

Distance is a scalar it doesn’t involve direction. It’s how far an object moves.
Displacement is a vector it includes both the distance and the direction of that straight line.

Question 28

What’s the difference between speed and velocity?

Answer 28

Speed is scalar

Velocity is a vector

Question 29

What’s the formula the links speed, time and distance?

Answer 29

Distance (m) = speed (m/s) x time (s)

S=vt

Question 30

What’s the speed of a person:

• walking
• running
• cycling

Answer 30

• walking: 1.5 m/s
• running: 3m/s
• cycling: 6m/s