# Interactions between objects

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• Created by: Katy **
• Created on: 03-01-14 15:48

## Newton's third law (1)

• This is when the action = the reaction.
• This is when the action is opposite to the reaction.
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## Newton's Third law (2)

↑ reaction - up thrust from chair (equal)

↓ action - weight of person (equal)

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## Newton's Third law (3)

↑ reaction - movment (less)

↓ action - gas (more)

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## Newton's Third law (4)

reaction - recoil (more)

→ action - bullet (less)

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## Newton's Third law (5)

↑ reaction - movement (less)

↓ action - jet gas (more)

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## Energy & Energy transfer

Energy Conservation:

• energy is not created / destroyed only transferred.
• heat is created & lost into the environment (dissapated).

Work done:

• = applied force x distance
• applied force can be resistance / friction

Kinetic Energy:

• = mass x (velocity)2

Gravitational Potential Energy (energy due to the change in height):

• = mass x gravity x change in height
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## Energy Changes

Lifting ↑:

• Work done-

= force x distance

= weight (mass x gravity) x height

Falling:

• Gravitational potential energy (orginal) -

= mass x gravity x change in height

• Gravitational potential energy (lost in fall) -

= mass x gravity x change in height - gained kinetic energy

• Gravitational potential energy lost = gained kinetic energy

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## Car Safety (1)

Killing speeds:

• increasing car speed = bigger chance of being killed

Speed Restrictions:

• speed  cameras - white lines & 2 cameras
• speed bumbs

Safety:

• in a collisionspeed /velocity of car changes to 0
• in a colisionchange of momentum (mass x velocity before - mass x velocity after)
• greater inital velocity before impact = greater momentum change
• greater inital velocity before impact = greater impact force
• slower velocity before impact = less damage
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## Car Safety (2)

Safety Devices:

Force = result of inital velocity/time for car to stop

• greater time = smaller impact

Seat belts & Air bags:

• extend time before person (brain) stops
• seat belts - stretch
• air bags - soft surface

Crumple Zone:

• front of modern carscollapse on impact
• extends time for car to stop

Protection:

• cage - area inside the car which remains unchanged in a collision

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## Car Safety (3)

Stopping distance:

• Thinking distance is increased by - car speed
• Thinking distance is affected by driver -

♦tired

♦drugs

♦alcohol

♦distractions

♦sat nav

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## Car Safety (4)

Braking distance is increased by -

• car's kinetic energy
• mass

Braking distance is affected by the car -

• warm tyres
• brakes
• suspention

Braking distance is affected by the road-

• surface (wet / ice / broken)

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## Car Safety (5)

Thinking distance:

= speed (of car) x time (thinking)

• greater speed = greater thinking distance
• longer thinking time = greater thinking distance

Braking distance:

• inital kinetic energy of car = (brake) force x (braking) distance
• brakes convert kinetic energy of car → heat
• brake force = friction of tyres / brakes / brake pods
• smaller brake force = longer brake distance
• greater mass = longer braking distance
• greater speed = longer braking distance

speed x2 = braking distance x4

kinetic energy = brake force x braking distance

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