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Check yourself: physical phenomena
Textbook: Part 2, pp. 98–99
GoalReview the unit “Physical phenomena and forces”: kinds of phenomena, motion, speed, gravity, friction and elastic force.
New words
force · kuchspeed · tezlikfriction · ishqalanishelasticity · elastiklik
Explanation
Review. In a physical phenomenon the substance does not change: they are mechanical, thermal, light, sound, electrical and magnetic phenomena. Speed is distance in a unit of time: distance = speed × time. Force starts, stops or reshapes a body and is measured in newtons. The three main forces: gravity pulls bodies down; friction hinders sliding between touching surfaces; elastic force restores a stretched or squeezed body to its shape. Mass is measured in kilograms and force in newtons — they are different quantities.
Worked examples
A parachutist: gravity pulls down, air resistance slows the fall.
Class activity
A game: act out one everyday example for each force (gravity, friction, elasticity) and let classmates guess which force it is.
Practice
1
Name the three main forces.
Gravity, friction and elastic force.
2
Speed 20 km/h, time 3 h. Distance?
60 km.
3
In which units are mass and force measured?
Mass in kilograms, force in newtons.