5: Forces

Question 1

define the moment of a force.

Answer 1

the turning effect of a force

Question 2

what is the equation to calculate the moment of a force?

Answer 2

moment of a force (Nm) = (perpendicular) distance (from the pivot to the line of action), in (m) x force (N)

Question 3

define pivot

Answer 3

the point at which something can rotate or turn, also known as the fulcrum

Question 4

what are the moments about a pivot like if the object is balanced?

Answer 4

the total anticlockwise moment is equal to the total clockwise moment

Question 5

what two things can be used to transmit the rotational effects of forces?

Answer 5

a lever; a gear system

Question 6

what (3 things) do levers have?

Answer 6

a pivot;
an effort (force used to move a load over a distance);
a load (the overall force exerted, usually by a mass or an object, on a surface)

Question 7

what are levers?

Answer 7

force multipliers - increase the force acting upon a load, without increasing the effort

Question 8

how would you increase the force on a load (using a lever)?

Answer 8

use a longer lever to increase the perpendicular distance from the pivot to increase the overall force

Question 9

what is newton’s second law (using momentum/ momentum change)?

Answer 9

force (N)= momentum change (kgm/s) / time (s)

Question 10

how can you decrease the force needed to make an object decelerate/accelerate?

Answer 10

decrease the overall momentum change; increase the collision/impact time

Question 11

what is impact force equal to?

Answer 11

it is equal to the change of momentum per second

Question 12

what is the centre of mass of an object?

Answer 12

the single point on the object where all of its mass can thought to be concentrated

Question 13

where is the centre of mass of a regular shaped object?

Answer 13

it is located at the geometric centre

Question 14

how do you find the centre of mass of an irregular shaped object?

Answer 14

attach a boss and clamp to a retort stand. put the optical pin in the cork and suspend the object from the pin and attaching it to the boss and clamp. also suspend a pendulum bob from the optical pin by using a string. now you can draw a line in line with the string. now do the same, but suspend the object from a different point and draw the line again. the point at which the lines cross is the centre of mass.

Question 15

what (3 things) do gears do?

Answer 15

transfer the moment of a force (aka torque); change the speed of a turning mechanism; change the axis of rotation - change linear motion into rotation, vice versa

Question 16

what are the ratios of gears?

Answer 16

ratio of moments = ratio of teeth = ratio of radii

Question 17

what is the equation for pressure?

Answer 17

pressure (Nmsquared or Pa) = force (N) / area (msquared)

Question 18

why do sharp scalpels cut more easily than blunt ones?

Answer 18

it has a smaller area of contact so the pressure when the same force is applied is greater, so it has a greater cutting effect.

Question 19

what happens when a low gear in a car is chosen?

Answer 19

when a low gear is chosen: a small gear wheel driven by the engine shaft is used to turn a large gear wheel on the output shaft - this shaft therefore turns slower than the engine shaft, but the turning effect is greater. low gear gives low speed and a high turning effect.

Question 20

what happens when a high gear in a car is chosen?

Answer 20

when a high gear is chosen: a large gear wheel driven by the engine shaft is used to turn a large gear wheel on the output shaft - this shaft therefore turns faster than the engine shaft, but the turning effect is lower. high gear gives high speed and a low turning effect.

Question 21

what is the equation for density?

Answer 21

density (kg/mcubed) = mass (kg) / volume (mcubed)

Question 22

how does the pressure in a liquid change w depth?

Answer 22

it increases.

Question 23

what does the pressure of a liquid depend on?

Answer 23

it depends on the density of the liquid - liquids w lower densities have lower pressures.

Question 24

what is the equation to calculate the pressure at the base of a liquid?

Answer 24

pressure (Pa) = height (m) x density (kg/mcubed) x gravitational field strength (N/kg)

Question 25

what is the equation to calculate the pressure at the surface of a liquid?

Answer 25

pressure (Pa) = force normal to a surface x area of that surface