Doc Brown's Revision  KS3 Science

PHYSICS Unit 7K Forces and their effects

What the Quiz is based on - original work schemes - programmes of study

and the quizzes will be adapted to suit the NEW National Curriculum for KS3 Science

All of KS3 Science is now under review

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In this unit pupils:

consolidate and build on their concept of force and its measurement

identify the origin of friction, air resistance, upthrust and weight and describe situations in which these forces act

distinguish between mass and weight

use the concept of speed

relate forces acting to changes in motion

identify situations in which forces are balanced and unbalanced

In scientific enquiry pupils:

consider why it is important to repeat measurements

measure distance, time and force including weight

construct and interpret line graphs and use them to make predictions

investigate floating in water of varying salinity, ensuring relevant variables are controlled

investigate friction between solids, ensuring relevant variables are controlled

This unit is expected to take approximately 8 hours.

Where the unit fits in

This unit uses ideas developed in the key stage 2 programme of study. It builds on ideas introduced in unit 4E ‘Friction’ and unit 6E ‘Forces in action’ in the key stage 2 scheme of work.

Together, this unit and unit 6E ‘Forces in action’ in the key stage 2 scheme of work can be used as bridging units.

This unit lays the foundation for unit 9J ‘Gravity and space’, unit 9K ‘Speeding up’ and unit 9L ‘Pressure and moments’. It also relates to unit 7D ‘Using control to control a display’, unit 8A(ii) ‘Exploring materials (resistant materials)’, and unit 9A(ii) ‘Selecting materials (resistant materials)’ in the design and technology scheme of work.

Expectations

At the end of this unit

in terms of scientific enquiry

most pupils will: make predictions about upthrust, test these and relate their findings to scientific knowledge; make suitably precise observations, including repeats to check reliability, and use these to plot graphs; investigate friction, identifying and controlling key factors

some pupils will not have made so much progress and will: make predictions about upthrust, test these and identify patterns in their results; with help plot graphs of their results; make relevant observations using appropriate equipment

some pupils will have progressed further and will: explain how they made a fair comparison in their investigation of friction; interpret their results on floating, using knowledge of balanced forces to explain conclusions; explain how the scales they chose and lines they drew on graphs enabled them to show data effectively

in terms of physical processes

most pupils will: identify directions in which forces act and describe situations in which forces are balanced; distinguish between mass and weight, giving examples; describe some ways of reducing friction and some situations in which friction is useful; describe what is meant by speed

some pupils will not have made so much progress and will: identify forces, eg friction, upthrust and weight; recognise that friction opposes motion, upthrust pushes upwards and weight pulls downwards; compare speeds qualitatively

some pupils will have progressed further and will: show how forces can combine to give a resultant effect which depends on both the sizes and directions of the forces; describe how weight is caused by gravity and how gravity is different on the Earth and on the Moon; explain contact friction in simple terms

Prior learning

know that pushes and pulls change the speed, direction or shape of an object

know how to measure distance and how to use a forcemeter to measure force in newtons

know that forces act in a particular direction and this can be indicated by arrows

have experience of the effects of a variety of forces, eg magnetic, gravity, friction, air resistance

Health and safety

Risk assessments are required for any hazardous activity. In this unit pupils:

use heavy weights

stretch springs and rubber bands

Model risk assessments used by most employers for normal science activities can be found in the publications listed in the Teacher’s guide. Teachers need to follow these as indicated in the guidance notes for the activities, and consider what modifications are needed for individual classroom situations.

Language for learning

Through the activities in this unit pupils will be able to understand, use and spell correctly:

words and phrases with different meanings in scientific and everyday contexts, eg drag, upthrust

words with a more precise meaning in scientific contexts than in everyday contexts, eg weight, mass, density

words and phrases relating to scientific enquiry, eg repeat reading, line of best fit

Through the activities pupils could:

identify the main points of a talk, TV programme, etc

Resources

Resources include:

immersion tank for objects to float and sink in

scales marked in grams, kilograms and newtons, including personal scales

lubricants, eg car oil, graphite

videos/pictures of the effects of friction, and of a person floating in the Dead Sea or similar

Highway Code (stopping distances)

Out-of-school learning

Pupils could:

collect advertising and publicity material relating to streamlining and reducing friction, eg in cars, bicycles, sports clothing, oils and lubricants

think about buoyancy and what helps them to float when swimming

think about gravitational attraction when viewing films, videos and television programmes showing activities such as hang-gliding or skydiving

 Where do we come across forces? •   about a range of forces •   how to measure forces •   Review what pupils know about forces by presenting them with a number of quick activities, eg     – weighing objects with a forcemeter     – pushing an ice cube and a wooden block across a smooth surface     – tying or untying a knot in plastic and natural string     – explaining how the time taken for a piece of paper to fall varies with the amount it is crumpled up     – pulling strong magnets apart     – stretching a spring     and questions, eg     – What force is acting here?     – What is its direction?     – Why are the forces changing? •   Discuss observations and answers with pupils. •  identify forces, eg magnetic attraction, friction •  use a forcemeter •  explain the observations they make, eg the plastic string is smoother so there is less friction and it is easier to untie •   This activity is intended to help teachers find out what pupils know and understand about forces from work in key stage 2. Teachers will need to take this into account in later work. •   Pupils are likely to have encountered a range of forces at key stage 2 and to have measured them using a forcemeter. Why do things float? •   that when objects are immersed in water there is an upthrust on them •   to draw conclusions from experimental results •   that when objects float the upthrust is equal to their weight •   that density is mass divided by volume •   Present pupils with floating objects which they can push down to feel the upthrust pushing up. Extend the range of objects and ask pupils to predict which will float, and to weigh them in air and immersed in water. Compile a table of results and ask pupils to identify patterns and draw conclusions from these. Ask pupils to record their results and explanations, eg by annotated drawings showing the forces acting on the objects. Discuss pupils’ ideas with them, referring to the work of Archimedes. Encourage generalisations, eg light for size, and show how to calculate density. Displacement of water can be used to measure volume (refer again to Archimedes). •  state that all the objects weigh less in water than in air •  explain their observations in terms of an upward force from the water ‘cancelling out’ some of the downward force of the weight •  recognise that objects which float show a zero weight reading •  state that an object will float in water if it is less dense than water •   Pupils may have met the term ‘density’ but will need help with calculations. •   Pupils will measure the density of objects using displacement in unit 8H ‘The rock cycle’. •   Archimedes checked the purity of a gold crown by measuring its volume by displacement.

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