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St Aloysius 2020-21 Physics 1Phy3 (JXC) > S1 Forces > Flashcards

S1 Forces Flashcards

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1
Q
  1. State the three main things that forces can change about an object.
A

Forces can change the shape, speed and direction of travel of an object.

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2
Q
  1. Give an example of forces changing shape, speed and direction.
A

One example each from below (or other equivalent):

When you squash a foam ball or stretch an elastic band the force causes a change in shape.

When you kick a ball or pull the brakes on a bike the force causes a change in speed.

When you turn the steering wheel in a car or a leaf blows in the wind the force causes a change in direction.

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3
Q
  1. State the unit of measurement of Force and its abbreviation.
A

Forces are measured in Newtons (N).

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4
Q
  1. What device measures the size of a force?
A

A Newton Balance measures the size of a force.

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5
Q
  1. State what friction is and what it does.
A

Friction is a force which opposes motion. This means that if an object is already moving it will try to slow it down and if it is stationary it tries to prevent it from moving

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6
Q
  1. What is the main type of energy produced by friction?
A

Heat energy is the main type of energy produced by friction.

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7
Q

7&8. Describe the factors affecting the size of the force of friction on an object.

A

The shape of an object: streamlined (or aerodynamic) objects experience less friction.

The material of the object: smooth surfaces experience less friction than rough surfaces.

The speed of the object: faster objects experience more friction.

The area of the object: larger areas experience more friction.

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8
Q
  1. Describe two situations where it is desirable to decrease friction.
A

We usually decrease friction when we want something to go faster.

For example:

To make a car go faster it is designed to be more streamlined.

Hinges are oiled to make doors open more easily.

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9
Q
  1. Describe two situations where it is desirable to increase friction.
A

We usually increase friction when we want something to slow down or not move.

For Example:

The brakes on a car are made of a special material so that when they rub against the wheels the car slows down.

The grips on the soles of your trainers help prevent you slipping.

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10
Q
  1. What is a gravitational field?
A

A gravitational field is the space around a planet where a gravitational force is experienced by a mass, attracting it towards the planet.

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11
Q
  1. What is weight?
A

Weight is a force and is the pull/force of gravity on a mass.

Its unit is the Newton (N).

It is measured by a Newton Balance.

It depends on the gravitational field strength, meaning it changes throughout the universe.

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12
Q
  1. What is mass?
A

Mass is the amount of matter in an object.

Its unit is the kilogram (kg).

It is measured by a balance.

It doesn’t change in size depending on where you are in the universe.

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13
Q
  1. W = m x 10 (on Earth)

(Define symbols and units)

A

W - Weight (N)

m - mass (kg)

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14
Q
  1. Example

Calculate my weight on Earth. My mass is 75 kg.

A 
m = 75 kg
W = ?
W = m x 10
W = 75 x 10
W = 750 N
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15
Q
  1. State the rules for drawing a graph in Physics.
A

In Physics we plot line graphs. These should contain:

  1. Two axes with regular spaced numbers along them starting from 0 (e.g. 0,1,2,3,…; 0,2,4,6,…; 0,5,10,15,…)
  2. Labels and units on each axis.
  3. The origin (where the axes meet) clearly marked with a 0.
  4. Points plotted correctly with an x.
  5. A best fit line (usually a straight line) following the trend, not necessarily going through every point.
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16
Q
  1. State what is meant by gravitational field strength and its value on Earth.
A

Gravitational Field Strength tells you the weight of each kg on a planet.

Its value on Earth is 10 N/kg.

17
Q
  1. W = mg

(Define symbols and units)

A

W - Weight (N)

m - mass (kg)

g - gravitational field strength (N/kg)

18
Q
  1. Example

Calculate the weight of a rocket of mass 20,000 kg on Saturn.

A

W = ?
m = 20,000 kg
g = 11.2 N/kg
(Sometimes given in the question but you will usually have to look it up in a table)

W = mg
W = 20,000 x 11.2
W = 224,000 N
19
Q
  1. Example

Calculate the mass of a drill which has a weight on Mars of 7.6 N.

A

W = 7.6 N
g = 3.8 N/kg
(Sometimes given in the question but you will usually have to look it up in a table)
m = ?

W = mg
7.6 = m x 3.8
(swap sides)
m × 3.8 = 7.6
(divide by 3.8 to get m on its own)
m = 7.6/3.8
m = 2 kg

20
Q
  1. Explain the term ‘balanced forces’
A

Balanced forces means that all the forces in one direction add up to the same value as all the forces in the opposite direction.

21
Q
  1. What do balanced forces have the same effect as?
A

When balanced forces act on an object, they have the same effect on its motion as no forces acting.

22
Q
  1. Describe an everyday situation which illustrate balanced forces.
A

For example, one of:

A parachutist falling with parachute open so that they are travelling at a steady speed. Their downwards weight is equal to their upwards air resistance.

A book sitting at rest on a table. Its downwards weight is equal to the upwards force from the table.

Often at the start of a tug of war both teams pull with the same force in opposite directions.

23
Q
  1. State Newton’s First Law of Motion.
A

Newton’s First Law of Motion (NI) states that objects remain at rest or continue to move at steady speed unless the forces on them are unbalanced.

24
Q
  1. Examples: Use Newton’s First Law of Motion to explain the motion of these objects:
  2. A parachutist falling with parachute open and travelling at a steady speed
  3. A book sitting at rest on a table
  4. At the start of a tug of war when both teams stay still
A
  1. A parachutist falling with parachute open travels at a steady speed because their downwards weight balances their upwards air resistance.
  2. A book sitting on a table stays at rest because its downwards weight balances the upwards force from the table.
  3. At the start of a tug of war both teams stay still because they both pull with the same force in opposite directions which is balanced forces.
25
Q
  1. Explain, using Newton’s First Law, how the use of seatbelts reduces the risk of injury during a car crash.
A

When you are in a car moving at speed, you are also moving at the same speed.

If the car stops suddenly and you are not wearing a seatbelt, by Newton’s First Law you will continue at the same speed until you hit something, probably causing injury.

If you are wearing a seatbelt, it applies a force to bring you to a stop over a longer time, reducing the risk of injury.

St Aloysius 2020-21 Physics 1Phy3 (JXC) (2 decks)

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