Physics - Forces Flashcards by Ruby Rose Burns

What is a Scalar quantity

Scalar quantities have magnitude (size) only

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Define vector quantity

Vectors have both magnitude (size) and direction

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What is a force?

A push or pull

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When are forces contact?

When objects are touching

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When are forces non-contact?

When objects are not touching

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Give an example of a contact force

Friction, air resistance, tension and normal contact force

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Given an example of a non-contact force

Gravitational force, electrostatic force and magnetic force

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What is weight?

The force acting on an object due to gravity.

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What is mass?

The amount of matter in an object.

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What is the equation linking weight, mass and gravitational field strength?

Weight = mass x gravity

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What is used to measure weight?

Newtonmeter

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Where does the weight of any object act from?

Centre of mass

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What is a resultant force?

A single force to represent multiple forces

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How do you calculate a resultant force?

Take away (opposite directions) or add (same direction) the forces.

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When is work done on an object?

When a force moves it a distance.

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What is equation linking work done, force and distance?

Work done = force x distance

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How many Joules is one Newton-metre?

1 joule

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What happens to the temperature of an object when work is done against friction?

It increases

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What happens to an elastic object up to the limit of proportionality?

Elastic deformation (It is able to return to its original length)

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What happens to an elastic object after the limit of proportionality?

Inelastic deformation (It will not return to its original length)

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What is the relationship between force and extension for an elastic object?

Directly proportional

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What is equation linking force, the spring

constant and extension?

Force = spring constant x extension

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Is distance a scalar or vector quantity?

Scalar

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Is displacement a scalar or vector quantity?

Vector

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Is speed a scalar or vector quantity?

Scalar

Is velocity a scalar or vector quantity?

Vector

What is displacement?

Both distance and Direction

What is the typical value of walking speed?

1.5 m/s

What is the typical value of running speed?

3 m/s

What is the typical value of cycling speed?

6 m/s

What is the equation linking distance, velocity and time?

distance = speed x time

When moving in a circle at constant speed, why is velocity constantly changing?

Direction changes, velocity is a vector

How do you calculate the speed of an object from a distance time graph?

by calculating the gradient

How do you calculate the distance travelled from a velocity-time graph?

Calculate the area under the curve/line of the selected time

How do you calculate acceleration from a velocity-time graph?

by calculating the gradient

What is acceleration?

The change in velocity over a given period of time

What is the equation linking acceleration, change of in velocity and time?

acceleration = change in velocity ÷ time

If an object is falling due to gravity what acceleration does it have?

9.8 m/s 2

What is the name for the constant speed a falling object reaches when the resistive force is equal to its weight?

Terminal velocity

What does Newtons first law say?

The velocity of an object will only change if there is a resultant force

Describe the motion of an object that is initially stationary, when the resultant force is zero

Remains stationary

Describe the motion of an object that is initially moving, when the resultant force is zero

Continues to move a constant speed in the same direction

What do we call the tendency of an object to remain in a steady state? (H)

Inertia

According to Newtons second law, what is the acceleration of an object inversely proportional to?

mass

What is the equation linking force, mass and acceleration?

Force = mass x acceleration

What is the inertial mass of an object? (H)

how difficult it is to change the velocity of an object

What is Newtons third law?

When two objects interact they exert equal and opposite forces on each other

What is stopping distance?

Thinking distance + braking distance

What is thinking distance?

distance travelled during reaction time

What is braking distance?

distance travelled once the brakes have been applied

What is a typical reaction time?

0.2 to 0.9 s

Give some factors that can affect reaction time

tiredness, drugs and alcohol, poor visibility

Give some factors that can affect braking distance

speed, worn tyres, worn brakes, icy roads, damaged roads

What is the law of conservation of the momentum?

total momentum before = total momentum after

What is equation linking the momentum, mass and velocity?

momentum = mass x velocity

Define Spring constant.

The stiffness of the spring

When moving in a circle in constant speed, why is velocity constantly changing?

Although the speed remains constant, direction changes, and since velocity is a vector quantity velocity changes

State Newton, second law

The resultant force acting on an object will cause the object to accelerate in the direction of this force

According to Newton’s second law, what is the acceleration of an object proportional to?

The resultant force

State three properties of a pair of forces which obey Newton’s third law

The forces are the same type, they act of two different bodies and have the same line of action

How is the force acting on an object related to its momentum?

Force = rate of change of momentum

How do safety, features such as air bags and seatbelts, reduce forces

Increase the time taken for the change of momentum

What is a moment?

Turning affect of a force

What is the equation linking moments, force and distance?

Moment of a force = force x distance

Describe the moment when an object is balanced

Clockwise moment. = anticlockwise moment.

How does a lever reduce the amount of force needed to create a moment?

By increasing the distance from the pivot

What is a fluid?

A liquid or a gas

What does pressure in a fluid cause?

A force at right angles to any surface

What is the equation linking pressure force and area?

Force = pressure x area

What is the equation, linking pressure, height, density and gravitational field strength

Pressure = height of the column x density of the liquid x gravitational field strength

Describe upthrust in terms of pressure

Pressure on bottom surface is greater than the pressure on the top surface

What happens to the density of the atmosphere with increasing altitude?

It decreases

What creates atmospheric pressure?

Collisions from air molecules

Why does atmospheric pressure decrease with high above ground?

Less air above as the height increases