Physics - 10 Force and Motion - 10.7 Safety First & 10.8 Forces and Elasticity

Safety helmet [3]

- increases impact time
- therefore decreases rate of change of momentum
- therefore decreases impact force and risk of injury

Car safety features [3]

- crumple zones
- seat belts
- air bags

Seat belt [4]

- increases impact time
- therefore decreases rate of change of momentum
- therefore decreases impact force and risk of injury
- spreads force out over chest

Air bag [4]

- increases impact time
- therefore decreases rate of change of momentum
- therefore decreases impact force and risk of injury
- spreads force out over upper body

- Thinking distance is ... to speed
- Braking distance is ... to ... speed

- proportional
- proportional, the square of

Crash mat [3]

- increases impact time
- therefore decreases rate of change of momentum
- therefore decreases impact force and risk of injury

Elastic

ability of an object to return to its original shape when forces deforming it are removed

Extension

increase of length from original length

Hooke's law

extension is directly proportional to force unless the limit of proportionality is exceeded

Limit of proportionality

limit beyond which an elastic object's extension is no longer proportional to the force that deforms it

Elastic limit

maximum stress a material can withstand without permanent deformation

Hooke's law equation

F = ke