2Y: Forces Flashcards
How do calculate weight on Earth?
To calculate the weight of an object on the surface of Earth = mass in kilograms × 10.
Find the weight of the following objects on the surface of the Earth:
(a) A rock of mass 10 kg
(b) A 100 g apple
(c) A 60 kg boy
Answer
(a) Rock = 10 kg × 10 = 100 N
(b) Apple: 100 g = 100/1000 = 0.1 kg, 0.1 kg × 10 = 1 N
(c) Boy = 60 kg × 10 = 600 N
Object g value (m/s2)
Earth 9.8 ≈ 10
Moon 1.6
Jupiter 25
Sun 274
Mars 3.8
Pluto 0.6
Using the above table, find the weight of a 5 kg mass on the surface of (a) Earth, (b) the Moon, (c) Pluto.
The formulae for weight is mass of object in kg × g value at that location
(a) Earth = 5 × 9.8 = 49 N
(b) Moon = 5 × 1.6 = 8 N
(c) Pluto = 5 × 0.6 = 3 N
This topic will be covered further in Chapter 37 The Earth, Sun and Moon.
How can you reduce Friction?
Friction may be reduced by:
Lubrication: Oil is placed between the two surfaces. Oil fi
lls the humps between two surfaces, stopping them catching each other.
Ball bearings: Small steel balls are placed between the two objects. The ball bearings roll over each surface instead of sliding, reducing the friction. These are used between a wheel and an axle.
Streamlining: As discussed before, the air can oppose the motion of moving objects. This is called air resistance. Air resistance can be reduced by streamlining. The shape of the object is designed to cut through the air efficiently. This is carried out with cars, rockets and planes.
What are the 3 disadvantages of Friction?
- *Friction slows things down**: A ship finds it difficult to travel through water because of the friction.
- *Friction wastes energy**: To overcome the force of friction, the engine of a car must burn a lot of fuel to maintain a car’s speed.
- *Friction causes wear**: Over a period of time the car tyres become worn and need to be replaced. The same happens on the soles of your shoes.
What is Weight?
The weight of an object is a measure of the force of gravity on it.
Objects with mass attract other objects with mass. This is a fundamental law of physics. You are attracted to this book and the book is attracted to you. However, because your mass and the mass of the book are fairly small, you do not notice this force.
This force becomes very significant when an object is placed near a massive object such as a planet. This force of attraction is called gravity. The greater the mass of the planet, the greater the force. We call the force of gravity on a body its weight.
What is Hooke’s Law?
The extension of a spiral spring is proportional to the applied force.
How was gravity discovered?
Legend has it that Isaac Newton (1642–1727) was at home resting under an apple tree when an apple fell from a tree to the ground. Newton asked himself why the apple always fell down. This sparked the idea of gravity in
his mind. The apple always fell towards the centre of the Earth because it was attracted to the Earth.
What is Friction?
Friction is a force that opposes motion.
Whenever one object slides over another object, friction tries to stop the movement. Friction always opposes the motion of an object. The rougher the two surfaces are, the greater the friction.
What are the difference between Mass and Weight?
- *Mass**: The amount of matter in a substance
- *Weight**: The measure of the force of gravity on a body.
- *Mass**: Remains constant everywhere in the universe. Can never be zero for an object.
- *Weight**: Depends on the amount of gravity in that location. Can be zero if no gravity present
- *Mass**: Unit = kilogram
- *Weight**: Unit = newton
What effect does Forces have on elastic objects?
Another effect of forces is that they can change an object’s shape. This is rather obvious with springs. When you pull on a spring with a force, it becomes longer. If the force is released, the spring will return to its original length.
- The more weight that is applied to the spring, the more the spring pulls back on the weight.
- When a weight is applied to the spring, the spring gets longer and it applies a force in the opposite direction to the weight. This force tries to restore the spring to its original length. This force is called the restoring force.
- The restoring force pulling up is equal to the weight pulling down. The forces are balanced so no acceleration takes place.
- If a spring is stretched too far, it loses some of its elasticity. The spring has been damaged. The spring is said to have been stretched beyond its elastic limit.
What 3 factors affect the weight of an object at the surface of a planet?
The weight of an object at the surface of a planet depends on three factors.
- The mass of the planet
- The distance from the centre of the planet (the radius)
- The mass of the object on the surface of the planet
The weight of a body can change slightly at different places on the Earth. This is because the Earth is not a perfect sphere. You are further from the centre of the Earth at the Equator and therefore the pull of gravity is less.
What is Force?
A force is anything that causes an object to accelerate (change velocity).
What are the 3 advantages of Friction?
Friction allows brakes to be used. Think of what happens to a moving car when it tries to stop on ice, which has very low friction.
Friction allows you to move. Friction between your shoe and the pathway allows you to move. This is why it is more difficult to walk on ice.
Friction slows down rain and hailstones. Without friction, rain and hailstones would cause a lot of damage as they would be moving at enormous speed
What is a Balanced and Unbalanced Force?
Forces that cancel each other out are said to be balanced.
- Balanced forces cause an object to move at a constant velocity.
- Unbalanced forces cause an object to accelerate (change velocity)
How can you measure Force?
Force can be measured using a newton meter (also called a force meter) or a force sensor.
