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Lucas Hayhurst

Institute of Physics Teacher Network Coordinator, Merseyside.

LHT@blueyonder.co.uk

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IoP main website www.iop.org

Practical work www.practicalphysics.org

Secondary school www.schoolphysics.co.uk

Advanced Physics advancingphysics.iop.org

Hyper Physics google “hyper physics”

Teacher community www.talkphysics.org

PTNC newsgroup networks.iop.org (click on PTNC)

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Newton’s 3 Laws of Newton’s 3 Laws of MotionMotion

Newton’s 3 Laws of Newton’s 3 Laws of MotionMotion

Newton’s First Law Law of Inertia

Newton’s Second Law F = ma

Newton’s Third Law Action Reaction

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ForceForce …the agency of change.

…changes the velocity.

…is a vector quantity.

...measured in Newton’s.

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Newton’s First LawNewton’s First Law Law of Inertia “A body remains at rest or (if

moving) moves in a straight line at a constant speed unless acted upon by an external resultant force.”

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What forces act on a ball in What forces act on a ball in flight?flight?

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Balanced Forces on a Spring Balanced Forces on a Spring (slinky)(slinky)

a) spring upb) fall down orc) stay where it is?

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CD HovercraftCD Hovercraft

Without the “hovercraft” effect from the balloon the external resultant force called friction causes the cd to slow down and stop.

When friction is compensated for there is no external resultant force once you’ve stopped pushing, so the CD travels in a straight line with a steady speed.

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Cartesian DiverCartesian DiverThink about the forces acting vertically: weight acting downwards and upthrust (bouyancy) acting upwards. The two forces are equal in size, so they cancel out when the diver is still (or moving with a steady speed).You make the diver accelerate upwards or downwards by changing the pressure.(Particle theory!)

upthrust

weight

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Terminal VelocityTerminal Velocity

The neodymium magnet very quickly reaches terminal velocity. If it is falling at a steady speed there must be no external resultant force. So some force must be balancing the weight. Do you know what it is?

?

Weight

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Newton’s Third LawNewton’s Third Law Action-Reaction

For every action force there is an equal and opposite reaction force

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MomentumMomentumThe astroblaster

A collision with the Earth!

4 balls collide with Earth with low velocity

1 ball rebounds with high velocity

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Law of Conservation of Momentum

Law of Conservation of Momentum

Results from a combination of NI and NIIResults from a combination of NI and NII

Collisions are described as ELASTIC (colliding objects have the same kinetic energy after the collision as they did before) orINELASTIC (energy is transferred as heat)

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Pressure = Force

Area

PressurePressure

Two of the same type of balloon, connected, one blown up a little more than the other. Initially the tap is closed. What happens when the tap is opened?

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Magdeberg HemispheresMagdeberg Hemispheres