Force

Scalar quantities have...

magnitude only

Vector quantities have...

magnitude and direction (an arrow) - force is a vector

Difference between contact and non-contact force

contact forces - the objects are physically touching

non-contact forces - the objects are physically separated.

Examples of contact forces

Friction

Air resistance

Tension in ropes

Normal contact force

Examples of non-contact forces

Gravitational force

Electrostatic force

Magnetic force

Difference between mass and weight

Mass is how much matter an object has and weight is how strong gravity pulls on the matter of a mass.

How to calculate weight?

Weight (N) = mass (Kg) x gravitational field strength (N/kg)

Centre of mass

A single point where the weight of an object may be considered to act

What is the relationship between the weight and mass of an object?

They are directly proportional.

What instrument is used to measure the weight of an object?

A calibrated spring-balance (a newtonmeter).

Resultant force

A single force that has the same effect as all the original forces acting together

Replacement of forces

A number of forces acting on an object may be replaced by a single force that has the same effect as all the original forces acting together

Balanced forces

Forces where the resultant force is zero.

Resolution of a single force

A single force can be resolved into two components acting at right angles to each other.

Effect of component forces

The two component forces together have the same effect as the single force.

The work done by a force on an object can be calculated using the equation:

work done (J) = force (N) × distance (m)

(moved along the line of action of the force)

1 joule =

1 newton meter

give examples of the forces involved in stretching, bending or compressing an object

- Stretching involves pulling forces (tension), such as a stretched rubber band or a hanging spring.

- Compressing involves pushing forces inwards, like squashing a metal can or springs.

- Bending uses combined push/pull forces

describe the difference between elastic deformation and inelastic deformation caused by stretching forces.

Elastic deformation is a temporary change in shape where an object returns to its original length after stretching forces are removed, such as a stretched rubber band. Inelastic deformation is a permanent change in shape, where the material remains stretched and does not return to its original form

explain why, to change the shape of an object (by stretching, bending or compressing), more than one force has to be applied - this is limited to stationary objects only

More than one force is required to change a stationary object's shape (stretching, bending, compressing) because a single force would merely cause the object to accelerate and move in that direction rather than deform.

force equation

force (N) = spring constant (N/m) × extension (m)

Describe the difference between a linear and non-linear relationship between force and extension

A linear relationship between force and extension follows Hooke's Law, creating a straight line on a graph where extension is directly proportional to force. A non-linear relationship occurs when the extension is not proportional to the force, shown as a curve, typically happening beyond the material's limit of proportionality

Describe examples in which forces cause rotation

Turning a nut with a spanner

Opening a door with a handle

What is the moment of a force?

The turning effect when a force causes an object to rotate about a pivot point

Moment of a force equation

moment of a force (Nm) = force (N) x distance (m)

The pressure at the surface of a fluid can be calculated using the equation:

Pressure (Pa) = force (N) / area (m^2)

The pressure due to a column of liquid can be calculated using the equation:

Pressure (Pa) = height of the column (m) × density of the liquid (kg/m3) × gravitational field strength (N/kg)

explain why, in a liquid, pressure at a point increases with the height of the column of liquid above that point and with the density of the liquid.

Liquid pressure increases with depth and density because pressure is caused by the weight of the fluid acting on a given area. A higher column of liquid or a denser liquid increases this downward weight, leading to greater pressure.

What is upthrust?

The upwards force exerted by a fluid on a submerged object

What is the atmosphere?

A thin layer of gases surrounding Earth

What creates atmospheric pressure?

Air molecules colliding with a surface

explain why atmospheric pressure varies with height above a surface.

Air pressure decreases with altitude because gravity pulls air molecules toward Earth's surface, making air denser at lower altitudes and thinner at higher ones

Typical values of speed for a person walking, running and cycling

walking ̴ 1.5 m/s

running ̴ 3 m/s

cycling ̴ 6 m/s.

A typical value for the speed of sound in air is...

330 m/s

Non-uniform motion

Motion with a change in speed, direction, or both

The average acceleration of an object can be calculated using the equation:

Acceleration (m/s^2) = change in velocity (m/s) / time (s)

The following equation applies to uniform acceleration :

(final velocity)2 (m/s) -(initial velocity)2 (m/s) = 2 ×acceleration (m/s^2) × distance (m)

terminal velocity

the constant velocity of a falling object when the force of air resistance is equal in magnitude and opposite in direction to the force of gravity

Newton's First Law

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

What is inertia?

The tendency of an object to resist a change in motion

Newton's Second Law

Resultant force (N) = mass (kg) x acceleration (m/s^2)

inertial mass

A measure of how difficult it is to change the velocity of an object

Newton's Third Law

For every action there is an equal and opposite reaction

What is Stopping Distance?

Thinking distance + braking distance

Reaction Time

Factors affecting braking distance

- how good you're brakes are

- how good tires are

- road conditions

Factors affecting thinking distance

- drugs

- alcohol

- tiredness

momentum equation

momentum (kg m/s) = mass (kg) x velocity (m/s)

Conservation of Momentum

In a closed system, the total momentum before an event is equal to the total momentum after the event.

Change in momentum equation

Force (N) = change in momentum (kg m/s) / change in time (s)

Explain how newton's third law applies to interaction between the kicking foot and ball.