Forces

Turning Moments

The size of the turning effect is called a turning moment. As Newton’s first law of motion states, an object will remain at rest if the forces are balanced. When the sum of the forces add to zero, a body will remain at rest or move at a constant velocity.

Demo

In this tutorial you will learn how to calculate the moments and apply the results to a real life situation for example forces acting on a see-saw.

The equation for this calculation is written like this:

$M = { \text F \; \text x \; \text D}$

Chilled practice question

The anticlockwise moment is is 75 Nm. What distance from the pivot must you place a 2.5 Kg mass for the clockwise and anticlockwise moments to equal ? Take gravity as 10N\Kg

Frozen practice question

You sit 2 m away from the pivot on a see-saw and your weight is 500 N. Your friend has a mass of 25 Kg. How far away from the pivot on the other side should they sit for the see-saw to balance ? Take gravity as 10N/Kg

Science in context

The size of the turning effect is called a turning moment.
Turning moment = force x perpendicular distance from the pivot.
As Newton’s first law of motion states, an object will remain at rest if the forces are balanced.
When the sum of the forces add to zero, a body will remain at rest or move at a constant velocity.

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Millie’s Magic Triangle

The ability to rearrange equations is the first step to successfully solve Physics calculations. Millie’s…

Calculation Master Method

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Moments

Forces can cause an object to rotate and the turning effect of the force is called a moment. If a resultant force acts on an object about a fixed turning point called the pivot or fulcrum it will cause the object to rotate e.g. using a spanner, a screwdriver, opening a door hanging on hinges.

Demo

In this tutorial you will learn how to calculate the moment in a real life example.

The equation for this calculation is written like this:

$M = { \text F \; \text x \; \text D}$

Chilled practice question

A 5 N force is applied to a spanner 15 cm from the pivot. Calculate the moment.

Frozen practice question

A screwdriver was used to open a tin of paint with a moment of 1.5 Nm exerted 25 cm from the pivot. What force was being applied ?

Science in context

Forces can cause an object to rotate and the turning effect of the force is called a moment. If a resultant force acts on an object about a fixed turning point called the pivot or fulcrum it will cause the object to rotate e.g. using a spanner, a screwdriver, opening a door hanging on hinges. M = F x d, where M = the moment of a force (Nm), = force applied (N) and d (m) is the distance from the pivot or fulcrum.

Millie’s Master Methods

Millie’s Magic Triangle

The ability to rearrange equations is the first step to successfully solve Physics calculations. Millie’s…

Calculation Master Method

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Force on a Spring

When a force acts on a spring it is stretched or compressed, its length will changes by an amount e from its original length.

Demo

In this tutorial you will learn how to calculate the force on a spring given its extension and spring constant.

Note-Some mobile devices may require you to tap full screen during playback to view video content.

The equation for this calculation is written like this:

$F = { \text k \; \text x \; \text e}$

Chilled practice question

Copy out the question and attempt to calculate the answer before watching the solution. Write down the equation and show all of your working, remember to add the units to your answer, this routine will guarantee you maximum marks in an exam. Mark your solution and correct if needed.

A spring is stretched 0.25 m, it has a spring constant of 20 N/m, calculate the force on the spring.

Frozen practice question

Copy out the question and attempt to calculate the answer before watching the solution. Write down the equation and show all of your working, remember to add the units to your answer, this routine will guarantee you maximum marks in an exam. Mark your solution and correct if needed..

A force of 10 N is applied to a spring and it extends by 20 cm, calculate its spring constant.

Science in context

When a spring is stretched or compressed, its length will changes by an amount x from its original length,  force  F = ke. The force the spring exerts is its restoring force, it acts to restore the spring to its original length.

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Pressure

Pressure can be calculated if you know the force applied to or by an object and the contact area. The units are newtons per square meter, or N/m2.

Demo

In this tutorial you will learn how to calculate the pressure exerted by an object if you have been given the force applied to the object and given area.

The equation for this calculation is written like this:

$P = { \text F \; \text / \; \text A}$

Chilled practice question

The base of a brief case has an area of 25 cm 2 and a mass of 5 Kg. Calculate the pressure exerted by the briefcase when placed on a surface. Take the force of Gravity as 10N/Kg.

Frozen practice question

An elephant exerts a pressure of 53500 N/m2 one of its feet has an area of 0.15 m2. Calculate the mass of the elephant. Take the force of Gravity as 10N/Kg.

Science in context

Pressure can be calculated if you know the force applied and the area using the physics equation, P = F/A. Pressure is equal to force divided by area, units are newtons per square meter, or N/m2.

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Force, Mass and Acceleration

An object of constant mass accelerates in proportion to the force applied.

Demo

In this tutorial you will learn how to calculate the force applied to an object if you are given its mass and acceleration.

The equation for this calculation is written like this:

$F = { \text m\; \text x \; \text a}$

Chilled practice question

Calculate the force applied to cannon ball which accelerates at 7m/s2 which has a mass of 5 Kg.

Frozen practice question

A rocket has a driving force of 15 N and a mass of 250 g. Calculate the acceleration of the rocket.

Science in context

Force (N) = mass (kg) Ã— acceleration (m/sÂ²). Therefore, an object of constant mass accelerates in proportion to the force applied.

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Forces and Work Done

The unit for work done is the joule (J), or Newton meter (N-m). One joule is equal to the amount of work that is done when 1 N of force moves an object over a distance of 1 m.

Demo

In this tutorial you will learn how to calculate the work done to move an object through a known distance.

Note-Some mobile devices may require you to tap full screen during playback to view video content.

The formula for this equation is written like this:

w = f x d

Chilled practice question

Copy out the question and attempt to calculate the answer before watching the solution. Write down the equation and show all of your working, remember to add the units to your answer, this routine will guarantee you maximum marks in an exam. Mark your solution and correct if needed.

How much work has been done if a car is pushed along the road 550 cm with a force of 400 N ?

Frozen practice question

Copy out the question and attempt to calculate the answer before watching the solution. Write down the equation and show all of your working, remember to add the units to your answer, this routine will guarantee you maximum marks in an exam. Mark your solution and correct if needed.

75 J of work is done pulling a trolley 150 cm. Calculate the force applied.

Science in context

Work can be calculated with the equationWork = Force Ã— Distance. The unit for work is the joule (J), or Newton â€¢ meter (N â€¢ m). One joule is equal to the amount of work that is done when 1 N of force moves an object over a distance of 1 m.

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The ability to rearrange equations is the first step to successfully solve Physics calculations. Millie’s…

Calculation Master Method

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Momentum

All moving objects have momentum. Forces can cause changes in momentum. The total momentum in a collision or explosion is conserved and stays the same. Car safety features absorb energy involved in a crash they slow down the collision thus reducing the force of impact.

Demo

In this tutorial you will learn how to calculate the momentum in a moving object.

The equation is written like this:

$P = { \text m\; \text x \; \text v}$

Chilled practice question

Calculate the momentum of a 1200 Kg vehicle travelling at 5 m/s.

Frozen practice question

A girl has a mass of 60 Kg. How fast is she moving if her momentum is 240 Kgm/s ?

Science in context

All moving objects have momentum. Forces can cause changes in momentum. The total momentum in a collision or explosion is conserved and stays the same. Car safety features absorb energy involved in a crash they slow down the collision thus reducing the force of impact.

Millie’s Master Methods

Millie’s Magic Triangle

The ability to rearrange equations is the first step to successfully solve Physics calculations. Millie’s…

Calculation Master Method

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Change in Momentum

All moving objects have momentum. Forces can cause changes in momentum. The total momentum in a collision or explosion is conserved and stays the same. Car safety features absorb energy involved in a crash they slow down the collision thus reducing the force of impact.

Demo

In this tutorial you will learn how to calculate the change in momentum and the affect it has on impact forces.

The equation is written like this:

$F = { mv \unicode{x2013} mu \over \text{t}}$

Chilled practice question

Calculate the force acting if there is a change in momentum from zero to 168 Kgm/s for 7 s.

Frozen practice question

A 50 kg gymnast is thrown in the air and travels at 5 m/s. The contact time to throw the gymnast is 0.5 seconds. Calculate the force acting on the gymnast.

Science in context

.All moving objects have momentum. Forces can cause changes in momentum. The total momentum in a collision or explosion is conserved and stays the same. Car safety features absorb energy involved in a crash they slow down the collision thus reducing the force of impact.

Millie’s Master Methods

Millie’s Magic Triangle

The ability to rearrange equations is the first step to successfully solve Physics calculations. Millie’s…

Calculation Master Method

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Uniform Acceleration

Uniform or constant acceleration is a type of motion in which the velocity of an object changes by an equal amount in every equal time period.

Demo

In this tutorial you will learn how to calculate uniform acceleration.

The equation is written like this:

${ \text v^{2} \; \text – \; \text u^{2} \; \text = \; \text 2as}$

Chilled practice question

A racing car travelling at 20 m/s decelerates uniformly at 1.5 m/s2 towards a slip road 100 m away. Calculate its velocity when it reaches the slip road.

Frozen practice question

A ball is dropped 12 m from the top of a building. Calculate the velocity of the ball when it hits the ground. Ignore any value for air resistance. Acceleration due to gravity is 9.8m/s2

Science in context

Uniform or constant acceleration is a type of motion in which the velocity of an object changes by an equal amount in every equal time period.

Millie’s Master Methods

Millie’s Magic Triangle

The ability to rearrange equations is the first step to successfully solve Physics calculations. Millie’s…

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Pressure in Fluids

Fluid pressure is exerted on the surface of an object in a liquid. This pressure causes upthrust . An object placed in a liquid will begin to sink. As it sinks, the liquid pressure on it increases and so the upthrust increases.

Demo

In this tutorial you will learn how to calculate the pressure on an object in a fluid at a known depth.

The equation is written like this:

$P = { \text h \; \text x \; \text p \; \text x \; \text g}$

Chilled practice question

Calculate the pressure 180 m below the surface of sea water. The density of sea water is 1025 Kg/m3. Use Gravity as 9.8 N/kg.

Frozen practice question

Calculate the density of a liquid if the pressure exerted is 5880 Pa at a depth of 75 cm, take the Gravitational field strength of the Earth to be 9.8 N/Kg.

Science in context

Fluid pressure is exerted on the surface of an object in a liquid. This pressure causes upthrust. An object placed in a liquid will begin to sink. As it sinks, the liquid pressure on it increases and so the upthrust increases.

Millie’s Master Methods

Millie’s Magic Triangle

The ability to rearrange equations is the first step to successfully solve Physics calculations. Millie’s…

Calculation Master Method

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