Forces and Energy Flashcards by Mr. Samuel

What is a resultant force

When a number of different forces act at a point on an object, they add up to a resultant force. This is the single force that has the same effect as all the original forces combined Simply add up the forces acting in a straight line in that direction (if it points in the opposite direction you must take it away)

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What are forces?

Pushes and pulls Measured in Newtons

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What do forces do?

Cause an acceleration or, Cause a direction change or, Cause a change of shape or All of the above

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What happens if the resultant force is zero? Will the object not move, slow down speed up or stay at the same speed?

The object will continue at the same speed, or if it was already stationary it will remain so This is Newton’s first law of motion.

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How are force (resultant force) mass and acceleration related?

Force = mass x acceleration This is Newton’s second law

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What are forces measured in?

Newtons (N)

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What is mass measured in?

kilograms, kg

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What is weight measured in?

Newtons, N It is the force due to gravity

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What is speed measured in?

meters per second m/s

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What is acceleration measured in?

meters per second per second m/s2

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What is speed?

A measure of how fast something is moving. It is the distance moved in a certain amount of time.

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What is velocity?

Speed is how fast you are moving Velocity is how fast you are moving is a particular direction. It is a VECTOR quantity. Examples 30km/h North

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What does the gradient (how steep the line is) of a distance time graph tell you?

The speed the object is moving at The steeper it is the faster it is moving

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What is deceleration?

Acceleration in the opposite direction to the motion (negative acceleration)

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What is acceleration

Rate at which velocity changes Change in velocity / time

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What does the gradient (how steep) of a velocity time graph represent?

Acceleration

What forces act on a car when it is moving?

Resistance, air resistance, driving force You may also have identified , weight and the normal reaction force from the road on the car

What is the resultant force of a car travelling at constant speed?

Zero

By Newton’s First Law if an object is travelling at constant speed there can be no resultant force acting on it. Otherwise it would be accelerating.

The same constant breaking force is used to stop a car; whatever speed it is travelling at to start with.

Explain what happens to the car’s stopping distance for higher speeds.

It will increase

In fact the braking distance goes up x4 when the velocity goes up x2.

What is the total stopping distance of a car made up of?

Thinking distance (reation time)

Braking distance

Which factors affect thinking distance

Tired

Drugs

Distractions (playing music, using mobile phone, chatting)

Age

Which factors affect braking distance?

Road conditions (ice, snow rain, type of road)

Condition of the tyres

Condition of the brakes

How much (approximately) does the stopping distance increase when the speed increases from 30mph to 50mph

at 30mph stopping distance is 23m

at 50mph it is 53m

increase is 30m

What is the definition of weight?

Force on a object due to gravity

Weight (N) = Mass (kg) x Gravitation Field Strength (10 N/kg on Earth)

As an objects fall through air which forces will act on it?

Gravity and Air resistance The faster the object fall the larger the air resistance will become

What is Terminal Velocity?

When the forces on an object, which is falling, reach an equilibrium (air resistance = weight) the object will no longer accelerate and has reached it's Terminal velocity As an object falls through the air (or fluid) it experience a resistive force called DRAG The faster the object falls the larger this force becomes It will continue to accelerate until the DRAG force is equal to the downward force The object cannot accelerate now and has reached TERMINAL VELOCITY

How does a parachute reduce a skydiver's terminal velocity?

Parachute creates a large air resistance (suddenly) This force is much greater than the weight cause a new resultant force which decelerates the skydiver As the speed decreases so does the air resistance on the parachute until a new lower terminal velocity is reached

What is the limit of proportionality?

The point beyond which increasing the force will cause a permament deformation. In other words the spring will no longer return to it's original shape

What is Hooke's Law?

Force = Sping constant x Extension F = k x e Force applied to an object is directly proportional to the extension

What is the definition of work done?

Another way of saying how much energy is transferred It is measured in Joules Work done = Force x distance W = F x d

What is the definition of Power

How much work is done (or energy transferred) in a given time In other words, a powerful machine can do a lot of work in a short space of time. Power (W) = work done (J) / time (s) or Power (W) = energy transferred (J) / time (s) It is measured in Watts (W)

What is Gravitational Potential Energy?

The energy an object possesses due to it's position in the graviational field. In otherwords how far off the ground it is. The higher it is the more energy it possesses GPE = mass x gravitational field strength x **_change_** in height GPE = m x g x h

What is Kinetic Energy?

The energy an object possesses due only to it's motion KE = ¹/₂ mass x speed² KE = ¹/₂ m x v²

What is the law of conservation of energy?

Energy cannot be created or destroyed It can only be transferred from one type to another

What 2 things does momentum depend upon?

The mass of an object The velocity of the object (remember that object which move towards each other at the same speed will not have the same velocity as one will be negative) momentum = mass x velocity Unit for momentum are **kg m/s**