Forces and motion mastery booklet.

Session 1: Forces.

Forces are responsible for a great deal of what happens in our universe. A force is any action that will change the speed, direction of shape of an object. Generally, forces occur when one body acts on another, there are lots of different types of forces. Some the two bodies must be touching for the force to be present these are called contact forces, in other cases one body can have an effect on another without having to be in contact, these are known as non-contact forces. The units for force are Newtons and can it can be measured using a Newton meter.

1. Complete the table below stating whether each of these forces is a contact or a non-contact force.

Force Name

Description Contact or non-contact

Thrust Forward push of an object moving on a solid surface Contact

Magnetism Attraction (pull towards) or repulsion (push away) of magnets and magnetic materials

weight Attraction between two objects with mass (Gravity)

Upthrust Upward push of water on an object

Normal contact

Upward push of a solid surface on a object

friction Force which slows objects moving along a solid surface

Water resistance

Force which slows objects moving through water

Air resistance

Force which slows objects moving through air

lift The force pushing up on a object as it moves through the air, caused by differences in air pressure.

Force Diagrams

Forces are often shown on diagrams to help us see what might happen, in these cases the forces are displayed as an arrow.

There are three important points to consider when drawing force diagrams.1. The tail of the arrow indicates where the force is acting2. The head of the arrow shows the direction the force is moving in3. The length of the arrow indicates the size of the force.

The tail of the arrow needing to be in specific places can often make the force diagrams overly complicated so one thing we can do is draw a free body force diagram, in these cases we assume all the forces act at the centre of the object so the diagrams would look like this instead:

There diagrams are much simpler to draw and still show us all the information we need to know.

2. Draw the forces onto these diagrams:

Answer these questions in your book.3. What is a force?

4. Give three examples of contact and non-contact forces?5. What are forces measured in?6. What piece of equipment can be used to measure forces?7. Finish the sentences below:

Some people think that gravity is a force they are wrong because…. Some people draw their force arrows with the heads pointing at the point

where the force is applied they are wrong because…..8. Name the forces that would be found on a runner moving forward9. Name the forces found on a bird mid flight10. Name the forces on a jet ski moving through the water11. Name the force on a tennis ball flying through the air.12. Draw the forces acting on a motorcyclist.13. Draw the forces acting on a speedboat14. Draw the forces acting on a plane

Session 2: Balanced and unbalanced forces.

There are three distinct types of motion; an object can be stationary; it can be moving at constant speed or it can be accelerating. Which of these an object will undergo depends on the forces acting on it. The motion depends on the resultant force, this is the overall force acting on a object when all of the forces acting have been combined.For an object that is stationary or travelling at constant speed the forces on the object are balanced, this means that it will have equal and opposite forces acting on it. These objects will have a resultant force of 0NAny object that is accelerating will have unbalanced forces, this means that there is a larger force acting in one direction than the other. The resultant force will no be 0N and the object will accelerate in the direction of the larger force.Balanced forces:

Unbalanced forces:

The resultant force can be worked out by adding together any forces acting in the same direction and subtracting any forces that are acting in the opposite direction:Examples:

Resultant force = 5N + 5N = 10N

Resultant force = 5N – 5N = 0N

Resultant force = 10N – 5N = 5N acting to the left

15.For each block: Calculate the resultant force State whether the block moves the left, right, up or down

A) B) C)

D) E) F)

5N

5N

5N5N

5N10N

20N 5N 12N 38N18N 2N

3N 18.5N

16.5N

298N

G) H) I)

16. For each picture that shows a moving cyclista) Calculate the resultant force and use an arrow to show the direction of this force.b) State whether the cyclist will accelerate, decelerate or travel at constant speed

The first one has been done for you

300N 600N 300N 340N 400N 400N

E.g.a) 600N – 300N =

300N b) accelerates

500N 450N 450N 400N 100N 101N

Answer these in your exercise book.

17. What is a resultant force?

18. Complete the sentences below:

10N

2.5N6.5N

11N

275N

480NN

196N

24.1N

27.6N

48.1N

309N

Some people think that when a striker kicks the ball during a penalty that there is a constant force pushing the ball forward, they are wrong because….

Some people think that when a car is travelling at a constant speed there must be a resultant force pushing forward, they are wrong because….

19. (a) A boat produces a thrust of 500N and experiences a drag of 300N, draw a force diagram to show this.

(b) Work out the resultant force acting on the boat.

20. A 50N, 100N and 150N are applied to an object, what is the maximum and minimum resultant forces possible?

21. Sally pulls a sledge in the snow at a constant speed.(a) Draw a force diagram to show this.

The sledge starts on the grass but moves onto the snow, friction is lower on the snow than it is on the grass.

(b) What will happen to the motion of the sledge if Sally pulls with the same force?

22. The diagram shows four forces acting on a plane in flight.

(a) Name the 4 forces acting on the plane?

(b) Which arrow represents air resistance?

(c) When the plane is flying at a constant height, which two forces must bebalanced?

(d) When the plane is flying at a constant speed in the direction shown, whichtwo forces must be balanced?

(e) Before take-off, the plane is speeding up along the ground. Which statement is true?

Force B is zero Force B is greater than force D

Force D is equal to force B. Force D is greater than force B.

(f) Which statement is true about the plane just as it leaves the ground?

Force C is zero. Force C is greater than force A. Force A is equal to force C. Force A is greater than force C.

Session 3: Gravity and weight.

Gravity is the force of attraction between pairs of objects. All objects have a gravitational field (gravity) around them but is only noticeable when HUGE objects are involved (like planets and stars). The force caused by the gravitational field of the earth pulling on your mass is your weight. This means that weight, mass and gravity are all related

It is very common for people to use the terms mass and weight incorrectly, mass is how much of a substance you have in kilograms (Kg), weight is the force acting on that mass measured in Newtons (N). The mass of a substance is fixed, but the weight will change depending on the strength of the gravitational field pulling on the mass. Gravitational field strength is measured in N/Kg. The larger a planet the stronger its gravitational field, so a mass’s weight will be higher on larger planets. Earth’s gravitational field strength on earth is 9.81N/Kg but this is often rounded to 10N/Kg.

The weight of an object can be worked out using the following formula:

Weight=mass×gravational field strength

Example question: What is the weight of a 5Kg mass on earth?

Weight = 5 Kg X 9.81 N/Kg

Weight = 49.05 N

Required practical:

Method

a) Collect a set of masses, a clamp and stand and a 10N Newton meter. b) Make sure the scale is set to zero before you begin. c) ang the newton meter from the clamp – with the newton meter hanging over the base of

the stand. d) Add the masses, one at a time, using the hanger. Record the reading on the newton meter

for each 100g mass. This is the weight – the force with which the mass is pulled down towards the centre of the Earth.

e) Repeat, adding 100g masses each time, up to 700g.

Results

Mass added (g) Weight (N)0

100200300400500600700

Plot a graph of your results on the axis below and draw a line of best fit.

0 100 200 300 400 500 600 700

Mass added (g)

7

6

5

4

3

2

1

0

Weight (N)

23. Why is it important to ensure that the newton meter is set to zero at the start? 24. Describe the relationship between mass and weight25. If you added a total of 1Kg, what reading would you expect on the newton meter?26. What sort of relationship is shown if there is a straight line through the origin?27. Complete the table to predict the mass or weight of other objects on Earth

Mass (kg) Weight (N)262

920

Floating and sinking.

An object will float or sink depending on it’s resultant force. In a liquid objects experience a for pushing them up, this is Upthrust, is the Upthrust is smaller than the weight hen their will be a resultant force downwards and the object will sink, if the Upthrust and the weight are equal there will be no resultant force and the object will remain in it’s current position. If the Upthrust is greater than the weight, then the object will float to the surface.

28. For A, B and C, label whether the object will float to the surface, remain stationary or skink.

Floating investigation.

For each of the objects given, use the newton meter to measure it’s weight in air and water then look to see if the object floats, copy your observations into the table below.

Answer these in your exercise book.

29. Explain what we mean by the term gravity.30. Explain the difference between mass and weight.31. Copy and complete these sentences in your book:

Some people ask how much something weighs but this is not the correct way of phrasing it because……

32. An astronaut has a mass of 90Kg, work out her weight on each of these planets:

Planet Gravitational field strength

(N/kg)*Mercury 3.7

Venus 8.9Earth 10.0Mars 3.7

Jupiter 23.1Saturn 9.0Uranus 8.7Neptun

e11.0

(a) State which planet he would weigh least on (b) State which planet he would weigh most on (c) Explain why his weight changes depending on the planet he’s on.

33. Calculate the weight of a 3kg object in a gravitational field with a strength of 10 N / kg.

34. Calculate the weight of a 5kg object in a gravitational field with a strength of 9 N / kg.

35. Calculate the weight of a 2.1 kg object in a gravitational field with a strength of 23.1 N / kg. Do this to 3 significant figures.

36. Calculate the weight of a 1200 g object in a gravitational field with a strength of 8.9 N / kg.

37. Calculate the weight of a 90 g object in a gravitational field with a strength of 3.7 N / kg. Do this to 2 decimal places.

38. Calculate the mass of an object 600N object in a gravitational field with a strength of 9.8 N / kg.

39. Calculate the mass of an object 4500N object in a gravitational field with a strength of 8.7 N / kg. Do this to 1 decimal place.

40. Calculate the mass of an object 3298N object in a gravitational field with a strength of 1.6 N / kg. Do this to 3 significant figures.

Session 4: Pressure.

When a force is exerted over a certain area we get pressure.

A good example of this is someone stepping onto snow, the weight of the person acts on the snow through the bottom of their shoes, creating a pressure on the snow. The greater the weight or force the greater the pressure will be. If the person was to stand on one foot the all their weight now acts through a smaller area so the pressure will go up.

Pressure can be calculated using the following formula:

Pressure= forcearea

In this formula force is measured in Newtons and area in meter3, this means pressure is measured in Newtons per meter3 (N/m3) this is also sometimes referred to as Pascals (Pa)

Example question – A 25N force is spread over a 5m3 area, what is the pressure?

Pressure = 25N / 5m3

Pressure = 5 N/m3

Some objects are designed to produce high amounts of pressure, such as a knife, having such a small surface area means a knife can easily produce enough pressure to cut into whatever it needs to.

Conversely to this snow shows has a large surface area, meaning they create a low pressure this means that they won’t sink into the snow.

Answer these in your exercise books.

41. Calculate the pressure of a knife with an area of 0.005m2 and a force of 40N.

42. Calculate the pressure of a shoe with an area of 0.02m2 and a force of 1400N.

43. Calculate the pressure of a car tyre with an area of 0.5m2 and a force of 14500N.

44. Calculate the pressure if a car crashes into a wall with 25000N and with a front area of 199cm2

45. A woman of mass 47.5kg on Earth stands in a pair of shoes with an area of 0.003m2. Calculate the pressure she is exerting on the ground. (Hint: First calculate her WEIGHT)

46. A child of mass 50.4kg on Earth lies on the bed with an area of 0.75m2. Calculate the pressure the child is exerting on the bed.

47. What pressure does a polar bear with a mass of 750kg, lying down covering 26 500cm2 apply to the ice?

48. Which of these objects exerts the most pressure? A ballerina with a mass of 60kg standing on point covering an area of 0.001m2 OR a tank weighing 8000kg with tracks covering 4.4m2?

49. Which of these is the highest pressure; 1N/m2 or 1N/cm2?

50. When 0.02m2 basketball hits a wall the pressure applied is 30 000N/m2. What force did the basketball hit the wall with?

51. A runner exerts 450,000N/m2 of pressure during a footstep. Her weight is 450N. What area of her foot was on the floor at the time?

52. A woman in stilettos, stands on a man’s foot with a force of 500N. If the stilettos have a surface area of 0.01m2, what pressure is exerted on the man’s foot?

53. A football has a surface area of 0.5m2. If the football hits a wall with a force of 200N, what pressure does the ball exert on the wall?

54. A bullet hits a pane of glass. If the bullet has a surface area of 0.5cm2, and strikes the glass with a force of 10,000N what pressure does this exert on the glass?

55. Which is best for walking on loose sand: a horse’s hoof or an elephants foot and why?

Session 5: Friction

When an object moves across a solid surface a force is produced that acts against the motion of the object, this force is called friction. If friction didn’t exist, it would be very difficult to stop any moving objects or even get them moving in the first place.

The amount of friction produced when an object moves depends on several things. The first is the speed of the object, the faster something moves the greater the frictional force produced.

The second is the surface itself, a smooth surface like ice will produce very little friction, hence so many accidents occur on ice, whereas a rough surface like carpet would produce much greater frictional forces.

The third factor is the mass of the object itself.

Friction investigation.

You are going to carry out a simple investigation to see how changing the mass of an object effects the frictional force produced when it moves.

You will attach a newton meter to a wooden block and pull the block along a surface. The reading on the newton meter will give you the friction created. You can then add masses on to the wooden block and see how it effects the frictional force.

56. State the independent variable:

57. State the dependant variable:

62. State 3 control variables:

1.

2.

3.

63. Write a prediction of what you think will happen to the frictional force when the mass of the

block is increased, explain your prediction.

Use the table below to copy down your observations.

Mass Added to Wooden Block /g Force Needed to pull the wooden block / N

0

100

200

300

400

500

600

700

800

900

1000

Session 6: Investigating speed.

You are going to plan and carry out an investigation into how changing the height of a ramp effects the time it takes a toy car to go down the ramp.

Your plan needs to include the following:

1. Independent variable2. Dependant variable3. 3 control variables4. A method

Now your investigation I planned you can carry it out. Use the table below to record your results.

Make sure to work out your average time taken (mean), this can be done using the following formula:

mean= (result 1+reuslt2+result 3 )number of reuslt

Once you have worked out your average you can plot a graph to see the relationship.

Table

Height of ramp (cm) Time taken for car to reach the end of the ramp (s)

Test 1 Test 2 Test 3 Mean

Graph

Conclusion: Write a conclusion to state hat your graph shows you about the relationship between the height of a ramp and the time taken for a object to move down it.

Session 6: Speed.

Speed is measure of how fast an object travels. The less time it takes an object to cover a distance the higher it’s speed must be. Speed can be calculated using the following formula:

Speed = distance ÷ timeGenerally, speed is measured in meters per second (m/s) this means that our distance should be measured in meters and the time taken in second. Below is some conversion to help you get your data into meters and seconds

1m = 100 cm = 1000 mm 1Km = 1000 m 1 minute = 60 seconds 1 hour = 60 minutes = 3600 seconds

Here are some typical speeds to help you get used to the units m/s.

Walking: 3 m/s Running: 6 m/s A car travelling at 30 mph: 13.5 m/s A car travelling at 60 mph: 27 m/s A jet travelling at 550 mpg: 245 m/s

64. Calculating speed

Example Partial example

Calculate the speed of a bicycle that travels 50m in 11 seconds1: list your VALUES (check units)S=? d=50m t=10sec

2:Write the EQUATION linking speed distance and time

Speed = distance ÷ time

3: ENTER value in

? = 50 ÷ 10

4:  RESULT S = 50 ÷ 10= 5

5: UNITS m/s

Calculate the speed of a unicycle that travels 100m in 25 seconds1: list your VALUES (check units)S=? d=__________m t=_________sec

2:Write the EQUATION linking speed distance and time

Speed = __________÷ _____________

3: ENTER value in

? = _________ ÷ ______________

4:  RESULT answer S = ________ ÷ _______=_____________m/s

5: UNITS ____________

65. Calculating distance

Example Partial example

Calculate the distance of a bicycle that travels at a speed of 5m/s for 10 seconds1: list your VALUES (check units)S=5m/s d=? t=10sec

2: Write the EQUATION linking speed distance and time

Speed = distance ÷ time

3: ENTER value in

5 = ? ÷ 10

4:  REARRAGNE AND RESULT 5 x10 = ? = 50

5: UNITS m

Calculate the distance of a unicycle that travels at a speed of 4m/s for 25 seconds1: list your VALUES (check units)S=________m/s d=__________m t=_________sec

2:Write the EQUATION linking speed distance and time

Speed = __________÷ _____________

3: ENTER value in

_________ = _________ ÷ ______________

4:  REARRANGE AND RESULT ________ x _______=? = ______

5: UNITS ____________

66. Calculating time

Example Partial example

Calculate the time it takes for a bicycle that travels at a speed of 5m/s to travel 10m.1: list your VALUES (check units)S=5m/s d=10m t=?

2: Write the EQUATION linking speed distance and timeSpeed = distance ÷ time3: ENTER value in

5 = 10 ÷ ? 4:  REARRAGNE AND RESULT 10 ÷ 5 = ? = 2

5: UNITS seconds

Calculate the time it takes for a unicycle that travels at a speed of 4m/s to travel 25 meters1: list your VALUES (check units)S=________m/s d=__________m t=_________sec

2:Write the EQUATION linking speed distance and timeSpeed = __________÷ _____________

3: ENTER value in _________ = _________ ÷ ______________

4:  REARRANGE AND RESULT ________ ÷ _______=? = ______

5: UNITS ____________

Answer these in your exercise book.

67. A skateboard travels 45m in 5 seconds. Calculate its speed

68. A kangaroo travels 66m in 10 seconds. Calculate its speed69. A bullet travels 3680m in 8 seconds. Calculate its speed.70. A stick on a lake travels 125m in 2.5minutes. Calculate its speed71. What is the speed of a dog which chases a postman 200m in 27seconds?72. A runner runs a 10km race. It takes them 45 minutes to finish. Calculate their average speed.73. A snail moves 31cm in 1 hour calculate its speed in meters per second (hint: lots of units to

convert first)74. A mouse runs at a speed of 6m/s for 11 seconds. Calculate the distance moved.75. A ball rolls at a speed of 7.5m/s for 27 seconds. Calculate the distance moved.76. A car travels at a speed of 45m/s for 80 seconds. Calculate the distance moved. 77. How far would a rocket travelling at 5000m/s move in 2 minutes?78. A ball is kicked into a goal at 14m/s. it takes 1.5s to reach the goal. How far away was it

when kicked?79. A comet travelling at 30km/s is watched by an astronomer for 11 seconds. Calculate the

distance moved by the comet.80. A marble rolled at a speed of 11m/s. How long did it take to roll 66m?81. A duck swam at 6m/s. How long did it take to swim 66m?82. A worm crawled at 0.05m/s how long did it take to crawl 1m?83. A stone is thrown off a 167m cliff into the sea. If it falls at 10m/s how long until you hear the

splash?84. A plane is travelling at 250m/s how long will it take to fly from Bognor to Glasgow 745km

away? Convert you answer into minutes please85. Usain bolt ran to a bus that was about to leave. He ran at 10.1m/s. The bus was 150m away

when he started and left 90 seconds later. Did he make it to the bus before it left?

Session 7: Distance-time graphs.

As well as calculating the speed of an object we can draw graphs to help us show how quickly an object is travelling.

These graphs are known as distance time graphs and show us how far an object has travelled in a given time.

These graphs will always have time on the x-axis and distance on the y-axis.

These graphs can be used;

to see if something is stationary, moving at constant speed or accelerating to see if something is moving forwards or backwards to calculate the speed something is travelling at.

When using these graphs we often need to talk about the gradient. The gradient of a graph is determined by the steepness of the line, the steeper the graph the larger the gradient.

Below is an example of a distance time graph.

86. Work out what the different shapes on the graph mean.

Section of the graph

What it shows us Shape of the graph

A Constant speed forwards Constant gradient, going up

B Constant speed backwards

C Stationary

D Constant speed forwards

E Decelerating

As mentioned earlier the speed of an object can be worked out from these graphs as well. The speed of the object is given by the gradient of the graph.

To work out the gradient of a graph we can use the following formula:

gradient= change∈ yaxischange∈x axis

Example: What is the speed for part A of the graph.

The change in y axis is worked out by looking at how much the line has gone up vertically by:

It has gone from 0 to 10m so the change in y axis is 10m

The change in the x-axis is worked out by looking how far the line has come across horizontally.

It has gone from 0 to 5 seconds, so change in x-axis is 5s.

gradient= change∈ yaxischange∈x axis

gradient=105

=2m /s

87. Work out the speed of the object at section D

Practice;

0 1 2 3 4 5 6 7 8 9 10 11 12 13 140

100200300400500600700800900

Time (seconds)

Dist

ance

tra

velle

d (m

)

88. State what is happening at points A, B, C, D and E. If the object is moving calculate its speed.

A

E

B

D

C

Section of graph

What is it the object doing / how fast is it travelling?

A

B

C

D

E

Drawing graphs.

When drawing distance time graphs there are a few important things to remember.

1. The time goes on the x-axis2. The distance goes on the y-axis3. Both axis need a scale, these should start at 0 and go up by the same number each time, you

should sort you scale so that the maximum number reached on the scale is just above what ever your highest data point is.

4. The line of best fit is drawn from point to point, this is one of the very few graphs in physics where we joining points together.

89. Draw your own distance-time graph.

Time (s) Distance travelled (m)0 05 10

10 2015 2020 4025 6030 6035 4040 2045 0

Comprehension questions – complete these in your exercise book.

90. Sketch a graph showing the following in your book: Dr Strange set out in his car this morning and travelled 500 metres in 30 seconds before

he stopped at the traffic lights for 100 seconds. He then joined the motorway and travelled 24,000 metres in 900 seconds. He then waited for 100 seconds at a roundabout. He then travelled the remaining 1000 metres in 100 seconds.

91. Sketch a graph showing the following in your book: Molly was so excited for her trip to the zoo that she ran the 800m to school that

morning. It only took her 100 seconds to get there. She jumped on the coach, where they all waited 600s until everyone was settled and

ready to go. They travelled 28,200 m and reached the zoo in 1800 seconds. When they arrived, the coach driver stopped for 480 seconds. During this time, the teachers saw that the zoo had been closed due to an emergency,

so they all had to return back to school. It took them 1600 seconds to make the return journey of 28,200m.

92. Which slope represents the faster speed?

93. Work out the speeds of A, B and C.94. Plot the following distance-time graph showing a cyclist riding around town:

Time (S) Distance (m)0 0

20 10040 20060 30080 300

100 600120 600140 400160 200180 0200 0

Distance (m)

Time (s)

40

400

2

20

AB

C

95. Use the graph you’ve drawn in the previous question to answer these questions.(a) How long was the cyclist stationary for?(b) Between which two times was the cyclist moving fastest?(c) Between which times was the cyclist moving forward?(d) Between which times was the cyclist moving backwards?(e) What was the speed of the cyclist between 0 and 60 seconds?(f) What was the speed of the cyclist between 80 and 100 seconds?(g) What was the speed of the cyclist between 120 and 180 seconds?

96. Some students ran a 100m race, here is some information about each student: Ashleigh starts running on the starting pistol. She runs the 100

meters in 12 seconds. How fast was Ashleigh? Bill starts running from the 25 meter mark. He reaches the finish

line in 15 seconds. How fast was Bill? Curtis starts running two seconds after the starting pistol. He

crosses the finish line at the same time as A. How fast was Curtis?

Darren runs the full 100 meters at 11 meters per second. He started running at the sound of the starting pistol. How long did it take Darren?

Elliot started running at the starting pistol at 10 meters per second, but gave up after 7 seconds. How far did Elliot run?

(a) Which runner was the fastest?(b) Which runner won the race?