P2.3 - Forces In Action

Question 1

How many forces are needed to change shape of an object

Answer 1

2 or more

Question 2

Plastic material

Answer 2

Does not return to its original shape after the force is removed - become deformed or distorted

Question 3

Elastic material

Answer 3

Returns to its original shape after the force is removed

Question 4

Hooke’s Law

Answer 4

Force is directly proportional to extension, within the limit of proportionality

Question 5

What is limit of proportionality

Answer 5

The point beyond which extension is no longer proportional to force

Question 6

Elastic limit

Answer 6

A force beyond which the material will not return to its original shape when the force is removed

Question 7

Spring constant

Answer 7

The ratio of force to extension

Can be said as a measure of the stiffness of a spring

Question 8

Equation for force exerted by a spring

Answer 8

Force (N) = spring constant (N/m) x extension (m)

F = k x e

Question 9

Equation for energy transferred in stretching

Answer 9

Elastic potential Energy (J) = 1/2 x spring constant (N/m) x (extension)^2 (m)

E = 1/2ke^2

Question 10

Gradient on a force and extension graph

Answer 10

Spring constant - the steeper it is the stiffer the spring

Question 11

area under force extension graph

Answer 11

Elastic potential energy

Question 12

A f.e graph for an elastic band would be non-linear

Answer 12

True - therefore doesn’t follow Hooke’s Law :)

good work keep going!

Question 13

Gravitational field

Answer 13

A region where a mass experiences an attractive force

Question 14

Gravity/weightequation

Answer 14

Gravity/weight (N) = mass (kg) x gravitational field strength (N/kg)

Question 15

What is gravitational field strength (aka gravity constant)

Answer 15

measure of the force on a 1kg mass when it is is a gravitational field

Question 16

What is weight?

Answer 16

Force due to gravity which acts upon an object

Question 17

Gravitational field strength of Earth

Answer 17

10 N/kg

Question 18

Gravitational field strength on the Moon

Answer 18

1.6 N/kg

Question 19

Resultant forces on planet equation

Answer 19

Resultant force (N) = Mass (kg) x acceleration due to gravity (m/s^2)

Question 20

What is gravitational potential energy (G.p.e)

Answer 20

The energy transferred to a gravity store when you lift an object in a gravitational field

Question 21

G.P.E equation

Answer 21

Gpe (J) = mass (kg) x gravitational field strength (N/kg) x height (m)

Gpe = mgh
G.f.s is always 10 on earth

Question 22

Moment

Answer 22

The turning effect of a force

Question 23

Moment equation

Answer 23

Moment (Nm) = force (N) x PERPENDICULAR distance (m)

Question 24

Moment is a vector

Answer 24

True - it is either CLOCKWISE or ANTI-CLOCKWISE

Question 25

What is the moment if the force is applied in line with the pivot?

Answer 25

Moment is 0 because it only applies when the force is applied across a PERPENDICULAR distance

Question 26

Perpendicular distance is indirectly proportional to force applied

Answer 26

Increase P.distance = proportional decrease in force applied (Vice versa)

Question 27

Principle of moments

Answer 27

When the anti-clockwise moment is the same as the clockwise moment about the pivot

Question 28

On a seesaw where would one with lower mass have to sit?

Answer 28

The person with the lower mass would have to sit further away from the pivot and the larger mass would have to sit closer to the pivot

Question 29

Lever

Answer 29

A force multiplier which transmits forces by rotating about a pivot. It reverses the direction of the input motion so it is opposite in the output

Question 30

Effort

Answer 30

The force that you exert in a lever (the input motion)

Question 31

Load

Answer 31

The force that the lever exerts of the load. (The output motion)

Question 32

If load closer to pivot

Answer 32

Less force needed (and vice versa)

Question 33

Mechanical advantage

Answer 33

Ratio of load to effort

Question 34

Mechanical advantage equation

Answer 34

MA (NO UNIT) = load/effort

Question 35

Gears

Answer 35

Like moment multipliers

Question 36

Mechanical advantage for GEARS

Answer 36

ma = output cog radius/input cog radius

Question 37

What is the perpendicular distance in a cog

Answer 37

The diameter

Question 38

If MA < 1

Answer 38

Speed multiplier HOW? - big gear goes to small gear - lower moment - output rotation is faster (because small one turns more within one cycle of the large one)

Question 39

If MA > 1

Answer 39

Torque multiplier HOW? - small bear goes to big gear - higher moment - output rotation slower (because within many cycles on the small one, the big one only does one)

Question 40

How did simple machines revolutionise the way things were done?

Answer 40

People were able to complete many tasks easily, using their own effort

Question 41

Pressure in a fluid equation

Answer 41

Pressure (Pa) = force @ 90 degrees to surface (N) / area of that surface (m^2) P = F/a

Question 42

Hydraulic machine

Answer 42

A simple machine which uses a liquid to transmit a force

Question 43

Composition of a hydraulic machine

Answer 43

2 pistons, a pipe with water- one piston is pushed, pushing the liquid in the pipe and then outputted by the second piston (Look @ figure 3 on pg 89)

Question 44

If the output piston is larger than the input one

Answer 44

Output force is larger

Question 45

If the output piston is smaller than the input piston

Answer 45

Output force is smaller

Question 46

Example of hydraulic

Answer 46

Car brake