Flashcards Palfi

Symbol: s

SI unit: m (meter)

Symbol: v

definition:  v = delta s/delta t    --> v=? const. or av. velocity

SI unit: ms^-1 

symbol: a

definition: a= delta v/delta t   --> a=const. or av. acceleration

si unit: ms^-2

- exactly one displacement s for each time t

- velocity v by: - the slope (for straight lines): v = delta s/delta t

                        - the slope of the tangent: v = limit of delta t aproaching 0 delta s/delta t 

- exactly one velocity v for ach time t

- acceleration a bvy the slope (of a straight line): a= delta v/delta t

- change in displacement delta s by the area under the curve

- velocity or speed

- 1 km h^-1 = 1000m/1h = 1000m/3600s = 1/3.6 s^-1

A body falls freely if it falls without friction (or friction is negligible). In this case, its motion is uniformly accelerated with acceleration a=g. The quantity g descibes the free fall and is called free-fall acceleratin or gravitational acceleration.

- symbol: g

-value: g= 9.81 m s^-2  --> at the surface of the earth

- si unit: ms^-2

Only by its effect, i.e.

- change in velocity, i.e. acceleration

- deformation, e.g. extending aspring or break a thread

- graphically: Move the tail of the second to the tip of the first. The vecor sum goes from the tail of the first to the tip of the last.

- algebraically: decompose each vector into its components and add the components.

- weight: vector F_W = m vector g

- normal reaction: vector F_R

- friction: vector F_F

- tension or compression: vector F_T

The weight is the force exerted by gravity of usually the earth: it is directed towards the centre of the earth.

Unit: N (Newtons)

vector F_W = m vector g

ex: A 100 g chocolate bar has a weight of about 1 N

If a body touches a support, the support exerts the normal reactin on the body. It acts perpendicular to the surface in direction of the body.

Sybol: vector F_R

Unit: N (Newtons)

ex: If you sit on a chair, the chair exerts a force, the normal reaction, on you.

Friction is a retarding force on a body. If the body is in motion, the firection in opposite the direction of motion. Friction can also act on a body at rest.

symbol: F_F

unit: N (Newtons)

ex: a block is pushed across a table. due to friction, the resultant force is less than the force it is pushed with.

Tension acts in a string, rope or thread. The direction is givben by direction of the string. A string, rope or thread can only pull on the body.  A rod can also push; in this case the force is called compression.

symbol: vector F_T

Unit: N (Newtons)

ex: You pull a sledge with a string. The force acting on the sledge is called tension. It acts in direction of the puller on the sledge.

An object at rest will stay at rest unless a resultant force is acting upon it. A moving object will continue to move at constant velocity along a straight line unless a resultant force is acting upon it.

The acceleration of a body is proportinal to the resultant force acting on the body and inversely proportional to its mass:

F_res = m vector a

If a body A exerts a force vector F on body B, then body B exerts a force of equal magnitude but opposite direction on body A.

Energy can neither be created nor destroyed, but only transferred from one kind to antother.

The SI unit for work and energy are the same: 1J = 1Ws (SI-units). Also commonly used is the kWh: 1kWh = 1000Wh = 1000W x 3600s = 3.6s = 3.6 x 10⁶Ws = 3.6 x 10⁶J

The SI unit for the power is W (Watt): 1 W = 1J/s