9.4 Mechanic Flashcards by nourhan :)

what is a moment?

A moment is a turning force.

Forces can make objects turn if there is a pivot.

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what is the equation for a moment?

Moment = Force x distance

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what do u need to calculate a moment?

the distance from the pivot that the force is applied

the size of the force applied

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how are things balanced?

the left-hand object acts in an anticlockwise direction, and the right-hand object acts in a clockwise direction. This is why the beam is balanced.

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what is Stopping distances?

In an emergency, a driver must bring their vehicle to a stop in the shortest distance possible

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equation for stopping distance

stopping distance = thinking distance + braking distance

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what is thinking distance?

thinking distance is the distance a vehicle travels in the time it takes for the driver to apply the brakes after realising they need to stop

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what is breaking distance?

braking distance is the distance a vehicle travels in the time after the driver has applied the brake

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what affects thinking distance?

tiredness
drugs
alcohol
distractions
speed

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what affects breaking distance?

poor road condition
wet or icy roads
poor vehicle conditions, such as worn brakes or worn tyres
mass of vehicle

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what happens when a force is applied to the brakes of a vehicle

there is work done by the friction between the brakes and the wheel. This reduces the kinetic energy of the vehicle, slowing it down and causing the temperature of the brakes to increase.

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types of energy

kinetic
nuclear
chemical
thermal
elastic
gravitational

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types of energy transfers

heating by radiation
mechanical/work
electrical/work
kinetic (particles)

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alpha radiation + ionising properties + penetrating powers + distance + charge

(alpha particles)2 protons and 2 neutrons
strongly ionising
stopped by paper
a few centimetres
positive (attracted to negative) (2+)

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beta radiation (process) + ionising properties + penetrating powers + distance + charge

high energy electrons form when a neutron splits into a proton and an electron
moderately ionising
stopped by aluminium
tens of centimetres
negative (attracted to positive) (-1)

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gamma radiation + ionising properties + penetrating powers + distance + charge

electromagnetic wave
not very ionising
stopped by concrete and lead
very large distances
neutral (0)

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what happens to radiation after it travels for very large distances?

All types of radiation become less intense as they travel further away from the radioactive material because the particles or rays become more spread out.

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what is half life

how long it takes for half the nuclei of a piece of radioactive material to decay.

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what happens to unstable nuclei

radioactive decay. they breakdown and change into a completely different type of atom.

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what is an isotope

Isotopes are the atoms of an element with different numbers of neutrons. They have the same proton number, but different mass numbers.

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can radiation be reflected?

yes. because they consist of charged particles, alpha and beta radiation can also be deflected by magnetic fields. Just as with electric fields, gamma radiation is not deflected by magnetic fields.

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ways of detecting radiation

photographic film (gets darker when it absorbs radiation)

- Geiger-Muller tube (Each time it absorbs radiation, it transmits an electrical pulse to a counting machine.)

natural sources of background radiation

cosmic rays - radiation that reaches the Earth from space
rocks and soil - some rocks are radioactive and give off radioactive radon gas
living things - plants absorb radioactive materials from the soil and these pass up the food chain

artificial sources of background radiation

x rays
nuclear weapons
nuclear power

alpha symbol is a nuclear equation

4 α 2

beta symbol in a nuclear equation

0 β- -1

neutron symbol is a nuclear equation

1 n 0

gamma symbol in nuclear equation

how are atoms always neutral?

The number of electrons in an atom is always the same as the number of protons, so atoms are electrically neutral overall.

what happens when an atom loses or gains electrons?

Atoms can lose or gain electrons. When they do, they form charged particles called ions: if an atom loses one or more electrons, it becomes a positively charged ion if an atom gains one or more electrons, it becomes a negatively charged ion

what is irradiation?

Exposing objects to beams of radiation is called irradiation.

what is contamination?

Contamination occurs if an object has a radioactive material introduced into (or onto) it.

irradiation properties

- Occurs when an object is exposed to a source of radiation outside the object. - Doesn't cause the object to become radioactive. - Can be blocked with suitable shielding or moving away. - Stops as soon as the source is removed.

contamination properties

- Occurs if the radioactive source is on or in the object. - A contaminated object will be radioactive for as long as the source is on or in it. - Once an object is contaminated, the radiation cannot be blocked from it. - It can be very difficult to remove all of the contamination.

what are the two types of radiation?

electromagnet and nuclear

where does nuclear radiation come from?

atomic nucleus from unstable isotopes

why is nuclear radiation released?

gives atoms greater stability

name a source of radiation

radon

define unstable nuclei

some nuclei are unstable, to become stable they fall apart; the particles and energy that are lost are called radiation

why is radiation dangerous?

radiation is ionising, it can damage DNA, causing cell mutations and therefore cancer

define 'ionising'

electrons leaving atoms

beta + decay (positron)

a proton becomes a neutron and a positron

positron symbol

0 β+ 1

equation for momentum

momentum = mass × velocity

what is inertia

the tendency of things to resist a change in motion

what is momentum

the strength or force that something has when it is moving.

how do we decrease an injury in a vehicle?

By increasing the amount of time it takes for momentum to change, it decreases the force, therefore decreasing the extent/ or severity of the injury

how do car safety features work?

Car safety features work by Slowing the rate of change of momentum

how do air bags work?

Air is gradually compressed, this takes time, slowing the rate of change in momentum

Why do we want to reduce the rate of change of momentum? (take longer to stop). Single choice?

It exerts a smaller force

How does a seatbelt reduce the force acting on your body in the event of a sudden stop?

It stretches slowly, which slows the rate of change in momentum

How do crumple zones reduce injury?

increase the amount of time a car takes to change momentum

A very large change of momentum in a short space of time means the car occupants will experience

a large force

what happens to the stopping distance when the speed increases?

As the speed increases, the stopping distance also increases