Chapter 3.5 - Newton's Laws of Motion Flashcards

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1
Q

Newtons 1st law

A

A body will remain at rest or continue to move in a straight line at a constant velocity unless an external force acts on it

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2
Q

Newtons 2nd law

A

The resultant force on an object is directly proportional to the rate of change of momentum of the object and the momentum change takes place in the same direction as the force

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3
Q

Newtons 3rd law

A

If object A exerts a force on object B, then object B will exert an equal and opposite force on object A

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4
Q

Equation for momentum

A

p=mv

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5
Q

Rate of change of momentum

A

Net force

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6
Q

In what way is F=ma a special case of F=Dp/Dt

A

F=ma is F=Dp/Dt but where the mass remains constant

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7
Q

Conservation of momentum

A

Assuming that no external forces act, total momentum is always conserved

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8
Q

Two equation for impulse

A

I=Ft

I=mv-mu

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9
Q

How is impulse related to momentum

A

It equals change in momentum

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10
Q

Area under a force time graph

A

Impulse

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11
Q

Rules for elastic collision

A

Momentum conserved

Kinetic energy conserved

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12
Q

Rules for inelastic collision

A

Momentum conserved

Kinetic energy not conserved

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13
Q

When can F=ma not be used

A

When objects are travelling close to the speed of light (resulting in their mass changing)

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14
Q

The essence of all car crash safety features

A

Increasing the time that it takes for the car and passengers to change their speed. This results in a lower force for the same impulse

Impulse ( P ) = Force x time

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15
Q

Crumple Zone and its effects (2)

A

Areas at the front of the car that crumple upon impact

  • Absorb some kinetic energy by deforming
  • Increase the time it takes for the car to slow down which reduces the forces on the passengers
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16
Q

Air Bags and their effects (2)

A

Cushions that inflate upon collision

  • Make passengers slow down more gradually
  • Stop passengers from hitting the dashboard
17
Q

Effects of a seat belt (3)

A
  • Holds the wearer in place
  • Absorb some kinetic energy by stretching
  • Increase the time it takes to come to a stop
18
Q

How forces in a crash are analysed

A

Crash tests

19
Q

Risks of seat belts (2)

A
  • Can cause bruising

- If the top part of the belt is placed across the neck in can cause injury in the event of a crash

20
Q

Risks of air bags (2)

A
  • If a passenger is not secured by a seatbelt then the airbag can hit the passenger hard
  • Can throw a rear facing child seat towards the car seat