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Physics > P2 - Forces > Flashcards

P2 - Forces Flashcards

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1
Q

What is a vector and scalar?

A

Vectors : have magnitude and direction (Forces, acceleration, velocity)

Scalar : Only has magnitude (speed, distance, mass)

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2
Q

Speed (Equation):

A

Speed = Distance / Time

Speed = m/s or km/h 
Distance = m or Km 
Time = s or h
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3
Q

Converting units (for speed)

A

Km –> m = multiply 1000
hr –> s = multiply by 60 (hr –> minutes ) than 60 again (minutes to seconds)

Km/h to m/s:
km/h x 1000 = m/h
m/h / 3600 = m/s

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4
Q

Acceleration (Equation):

A

Acceleration = change in speed / time

Acceleration = m/s^2
Change in speed = m/s
Time = s

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5
Q

What is contact and non contact forces?

A

Contact force: When object must be touching for force to occur (push and pull)

Non contact forces: When objects don’t need to be touching for force to occur (eg magnetism)

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6
Q

What is the resultant force?

A

It is the overall force on an object or point.

An object with zero resultant force (forces are balanced) is stationary or moving at a constant speed.

An object with a resultant force more than zero means forces are unbalanced.

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7
Q

Distance-time graphs:

A 
/ = constant speed
- = stationary
\ = constant speed
Curved line = acceleration
Gradient = speed
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8
Q

Velocity-time graphs:

A 
/ = acceleration
-  = constant speed
\ = deceleration
curved line = changing acceleration / deceleration
Gradient = acceleration
Area under lines = distance
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9
Q

What is Newtons 1st law?

A
  • An object will remain stationary or at a constant speed unless external forces act upon it - inertia
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10
Q

What is Newtons 2nd law?

A
  • if object with mass has a resultant force it will accelerate

This means: any resultant force will cause an acceleration

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11
Q

Force (Equation):

A 
Force = mass x acceleration 
Force = N
Mass = Kg 
Acceleration = m/s^2
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12
Q

What is friction?

A

Friction slows things down
If friction = driving force –> constant speed
If friction > driving force –> deceleration
If friction < driving force –> acceleration

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13
Q

What is terminal velocity in terms of skydiving example?

A

1) Skydiver in plane is stationary so there is no air resistance but there is weight
2) When out of plane, skydiver accelerates due to weight > air resistance
3) As acceleration increases, air resistance increases until weight = air resistance (new terminal velocity reached)
4) Skydiver pulls parachute to increase surface area and that increases air resistance - weight < air resistance (deceleration)
5) As skydiver decelerates, air resistance decreases until weight = air resistance (new terminal velocity reached which is slower than 1st terminal velocity)

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14
Q

What is Newton’s 3rd law?

A
  • When two objects interact the forces acted upon each other are equal and opposite.

Skater example:

1) When skater A (with mass 55Kg) pushes skater B (with mass 65Kg) they feel an equal and opposite force from skater B’s hand
2) both skaters feel same force in opposite directions so they accelerate away from each other
3) skater A will accelerate more than B as she has a smaller mass, so smaller inertia (force = mass x acceleration)

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15
Q

What is momentum + equations?

A

Momentum (Kgm/s) = Mass (Kg) x Velocity (m/s)

Force causes momentum hence:
Force = change in momentum / time

Momentum is always conserved:
Momentum before collision = momentum after collision

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16
Q

Weight (equation):

A

Weight (N) = Gravity ( N/Kg) x Mass (Kg)
F=mg
Gravity is always 10 N/Kg on Earth)

17
Q

Gravitational potential energy (Equation):

A

Gravitational potential energy (J) = mass (Kg) x Gravity(N/Kg) x height (m)

GPE = mgh

18
Q

Kinetic energy + Equation:

A

When an object is moving energy is transferred to its kinetic energy stores.

Kinetic energy (J) = 1/2 x mass (Kg) x Velocity^2 (m/s)

KE = 1/2 mv^2

19
Q

Work done + Equation:

A

Work is done when a force moves an object
Workdone (J) = force (N) x distance (m)
Work = Fd

20
Q

Power + Equation:

A

Power is the rate of doing work / Energy transfer

Power (W or J/s) = Work (J) / Time (s)
P = E/t

21
Q

What are the two types of deformation?

A

Elastic deformation: When the forces are removed from the object the object returns to its original shape.

Plastic deformation: When the forces are removed from the object the object doesn’t return to its original shape.

22
Q

Spring constant (Equation):

A

Force exerted by spring (N) = spring constant (N/m) x extension (m)
F=kx

23
Q

What is the relationship between force and extension?

A

Most objects deform elastically when force increases until the object they reach they reach their limit of proportionality. As force continues to increase, extension doesn’t continue to increase as the object continues to deform plastically.

24
Q

Work done and extension + energy transferred in stretching equation?

A

When a force deforms an object work is done.
Energy transferred in stretching (J)= 1/2 x spring constant (N/m) x extension^2 (m)
E = 0.5 kx^2

25
Q

What is moments + equations

A

Moments are the turn effect of a force

Moments = force (N) x distance (m)
M=fd
Distance is measured form the pivot

26
Q

How do you get maximum moment?

A

To get maximum moment push perpendicular

27
Q

How to you balance an object using moments?

A

If total anticlockwise moment = total clockwise moment the object will balance.

28
Q

What are levers?

A

Levers are force multipliers (eg wheelbarrow)

- Levers increase distance so less input force is required for same moment

29
Q

What are gears?

A

Gears Fit together to transfer turning effects
- When a force is applied to the smaller gear there is a small moment. When this gears applies a force to the larger gear next to it, the distance is larger from the pivot (it is a larger gear) and the moment is larger.

30
Q

How to calculate speeds and moments between gears?

A

Use gear ratios
Eg : If gear A has 16 teeth and gear B has 8 teeth. How many times will gear A turn for one turn of gear B?

1) Find gear ratio: 16:8 = 2:1
2) For every one turn of cog A, cog B will turn twice

31
Q

What is pressure + equation?

A

Pressure is the force per unit area

Pressure (pa) = Force (N) / Area (m^2)

32
Q

What is pressure in liquid?

A

Liquid pressure is caused by liquid particles hitting the side of the container causing a net force perpendicular to all surfaces.

33
Q

What are hydraulics?

A

Hydraulic are force multiplier - they use a small force to produce a larger force.

Hydraulics have two pistons (one with a smaller cross sectional area). Pressure is transmitted equally through liquid so pressure at both pistons are equal.

The 2nd piston has a larger area so using Force =Pressure x area the 2nd piston will have a larger force.

34
Q

What is the upward force in a spring?

A

Tension / spring force

35
Q

What are the SUVAT equations?

A 
S - Displacement 
U - Initial speed 
V - final speed
A - acceleration
T - Time 
V^2 = U^2 + 2AS 
V = U + AT 
S = UT + 1/2 AT^2
S = VT - 1/2 AT^2
S = 1/2 ( U + V ) T

Physics (9 decks)

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