# P4

These are important learn them for the exam

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## Speed

Speed means the distance travelled in a certain time.

# SPEED= DISTANCE/TIME

• The flat bit on a speed graph is where something is stationary/ stopped.
• The downwards bit means that something is going back to where it started
• Curves mean acceleration or deceleration
• A negative slope means going back to starting point.
• Speed is just a number.

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## Velocity

Velocity also includes direction; it is more useful beucase it measures motioon; 30mph north.

Velocity can be positive or negative; going in one direction could be 20mph and the opposite could be -20. they are going the same speed just different directions, but still away from starting point.

• Flat means travelling at a steady speed
• The steeper the graph means greater acceleration/ deceleration.
• Uphill means acceleration, downhill means deceleration, not comming back to start place.

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## Kinetic energy

Kinetic energy is the energy of movement.

Anything moving has kinetic energy. This depends on both the mass and its speed .

# Kinetic energyy= 1/2 x mass x velocity*

To increase kinetic energy, you have to increase its speed. This needs a force to exert its velocity and speed.

## Increase in kinetic energy= bit less then works done.

#### All falling objects convert from Gravitational Potential Energy to Kinetic Energy.

The further it falls, the faster it goes.

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## Forces and Friction

Forces occur when two objects interact; an "interacting pair"

If you push a wall it will push back at you just as hard; there is an "oposing force"

Objects on a surface area have a reaction force; moving objects experience friction.

There are three types of friction:

• Friction between solid surfaces which are gripping
• Friction between solid surfaces which are gliding past eachother
• Resistance or "drag" from fluids (liquids or gasses)

Different length arrows mean unballanced forces.

These arrows show the size and direction of forces.

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## Forces in Motion

If arrows are the same saze and opposite direction, it means the forces are ballanced. If there is a steady speed it also means that the forces are ballanced and so at zero.

Resultant force is very important . Forces acting on an object are often unballanced. The resultant force is the overall force on the object. This ditermines whether the change in motion is necesary. Velocity is the change in direction too; acceleration can mean both speeding up or changing direction at the same speed.

Acceleration means unbalanced forces; there is more force forwards then drag behind. Momentum is a vector quality like velocity.

the change in momentum depends on force.

# MOMENTUM=FORCE X VELOCITY

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## Work

"work done" means "energy transferred"

When a force moves an object, energy is transferred and work is done.

# WORK DONE= FORCE x DISTANCE

With a broom, the amount it has to be pushed into the floor to get it to move is the force, this multiplied by the distance it is moved= work done.

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## G.P.E is "height energy".

It is the energy stored in an object when you raise it above the force of gravity.

When something falls, it is converted from G.P.E to Kinetic Energy.

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