Moments Levers and Gears

Question 1

Moment

Answer 1

-turning effect of a force around a fixed point (pivot)

Question 2

Examples of moments:

Answer 2

-door opening around a hinge
-seesaw
-scissors
-spanner

Question 3

Unit of moments

Answer 3

Newtonmetres (Nm)

Question 4

How to calculate the magnitude of a moment?

Answer 4

moment = force (N) x distance (m)

Question 5

Example moments question:
A force of 40N is applied to a spanner to turn a nut
The perpendicular distance is 0.3m
Calculate the moment

Answer 5

40N x 0.3m
12Nm

Question 6

If an object is balanced….

Answer 6

…the total clockwise moment about the pivot = the total anticlockwise moment about the pivot
-called principle of moments

Question 7

Example balanced moment question:
A parent and child are at opposite ends of a playground see-saw. The parent weighs 750 N and the child weighs 250 N. The child sits 2.4 m from the pivot. Calculate the distance the parent must sit from the pivot for the see-saw to be balanced.

Answer 7

-child’s moment = 2.4m x 250 N= 600Nm
-parents moment must also be 600Nm
-600Nm/750N= 0.8m

Question 8

Pivot

Answer 8

-point around which something can rotate or turn

Question 9

Effort

Answer 9

-force applied to move a load over a distance

Question 10

Load

Answer 10

-force or weight that needs to be moved or lifted

Question 11

The longer the lever, the further the effort acts from the pivot so…

Answer 11

….the greater the effect of the force on the load will be.

Question 12

Example lever question:
A solid beam 0.5 m long is laid across a pivot to form a simple lever. The pivot is 0.1 m from the end of the beam. Calculate the heaviest load that could be lifted using a force of 500 N.

Answer 12

effort = 500N x 0.4m= 200Nm
load = 200Nm/0.1m = 2000N

Question 13

Gear

Answer 13

-toothed wheel rotating around an axle, transmitting force and altering speed/direction in a system.

Question 14

Axle

Answer 14

-rod through a wheel/gear that they rotate around

Question 15

If one gear turns…..

Answer 15

…the other also turns.

Question 16

Where the gears meet, the teeth must both move in the ____ direction, so the gears rotate in ________ directions

Answer 16

-same
-opposite

Question 17

If the driven gear is made larger is will rotate more ______ but with a _____ moment. This is called a ___ ____ ratio.
Why?

Answer 17

-slowly
-greater
-low gear
-it take up more space so it will do less frequent turns but it will also move with a greater moment, as the perpendicular distance from the pivot is greater

Question 18

If the driven gear is made smaller it will rotate more ? but with a ? moment. This is called a ? ratio
Why?

Answer 18

-quickly
-smaller
-high gear
-it take up less space so it will do more turns but it will also move with less force as the distance from the pivot is smaller

Question 19

Example gear question:
A gear with a radius of 0.1 m is turned by a gear with a radius of 0.05 m. The moment of the smaller gear is 20 Nm. Calculate the moment of the larger gear

Answer 19

0.05m x ?N = 20Nm
400N
400N x 0.1M = 40Nm

Question 20

Two things you can do to get a bigger moment

Answer 20

-increase the size of the force
-make the distance between force and the pivot bigger

Question 21

If the turning forces of a system are balanced…

Answer 21

….there must be the same clockwise movements as there are anticlockwise movements.
sum of clockwise movements = sum of anticlockwise movements.

Question 22

Mass

Answer 22

-amount of matter in an object (kg)

Question 23

Weight

Answer 23

-gravitational force acting on an object

Question 24

Equation for weight

Answer 24

weight = mass x gravitational field strength

Question 25

Centre of mass

Answer 25

-point in a body or system of bodies at which the whole mass may be considered as concentrated > this may be found at the geometric centre for regular shapes

Question 26

Centre of gravity

Answer 26

-point from which the weight of a body or system of bodies may be considered to act

Question 27

How does a lever act as a force multiplier?

Answer 27

-it makes the perpendicular distance between the pivot and the effort greater -if the pp distance between effort and pivot is greater than distance between effort and load >the force applied on the load is greater than the effort force

Question 28

How do gears work?

Answer 28

-turning force is applied to one wheel -interlocking wheel turns adjacent wheel in opposite direction -cogs prevent wheels from slipping

Question 29

Fill in the blank: A lever amplifies an input force to lift a _______.

Answer 29

Load

Question 30

What is the difference between center of mass and center of gravity?

Answer 30

Center of mass is the point where mass is evenly distributed; center of gravity is the point where weight is evenly distributed.

Question 31

What determines the moment of a gear wheel?

Answer 31

-size of the wheel

Question 32

Describe the moment and speed of a larger gear being driven by a smaller gear

Answer 32

-larger wheel will rotate more slowly but will also produce a larger moment

Question 33

What will happen if child B moves closer towards the pivot?

Answer 33

-clockwise movement of Child B decreases -so it is less than the anticlockwise moment of child A -child a moves downwards -child B moves upwards