FORCES Flashcards
Who was the first person to suggest that forces follow certain rules?
Sir Isaac Newton
What is a force?
A push or pull on an object
Everything you do uses forces. You can’t see them but you can often see the effect they have.
What are Newton’s Laws of Motion
He suggested that forces can:
- Change the shape or size of an object
- Make things go faster or slower
- Change the direction in which something is moving
What happens when you are lifting an object?
You are lifting it against a force
What is the object’s force?
It’s weight which pulls it down
What does weight mean?
How heavy something is
Weight is a force that pulls things in which direction?
Downwards
Define weight
The force of gravity on an object
Heavy objects are pulled down with…
A bigger force than lighter objects
What do we measure weight and all other forces in?
Newtons
What is gravity?
The force that pulls everything towards the centre of the Earth
Describe the Moon’s gravity
Also pulls things towards it centre but is weaker than the Earth’s by about 1/6
Define BALANCED FORCES
When 2 forces are the same strength, but working in opposite directions
Define GRAVITY
The force of attraction between any two objects.
The Earth is very big and so has a very large gravity pulling everything down towards it.
Define MASS - 3 points
- The amount of matter that something is made of.
- It is measured in grams or kilograms.
- Mass does not change if you go into space or another planet.
Define NEWTON
The unit of force (N)
Define UNBALANCED FORCES
When 2 forces working in opposite directions are not the same strength.
Define WEIGHT - 2 points
- The amount of force with which gravity pulls something towards the Earth.
- It is measured in Newtons (N)
Define STATIONARY
Not moving
What does mass tell us?
About the amount of matter that something contains
How do you calculate the weight of an object on the moon? - 2 points
You divide its weight on Earth by 6
1kg weights about 1.5N on the Moon
What effect does balanced force have in the movement of an object?
There is NO change in movement
What effect does unbalanced forces have in the movement of an object?
Change the speed AND/OR
The direction of moving objects
Think of a see-saw
When the forces are balanced…
The object is not moving
If the upthrust (or push up) of the air is equal to the force of gravity pulling down a balloon what happens?
The balloon remains suspended in the air.
If a strong wind starts blowing from behind a boat, what effect does this have on how the boat moves?
The wind propels the boat forward
If after a short time, the force of the wind is still acting, the boat moves at a steady speed, why is this?
The water resistance starts to slow the boat down, but the wind is still pushing the boat
The force on an object are unbalanced when…
One of the forces is bigger than the other
How is the size of force shown on a drawing?
By the length of an arrow, the longer the arrow means the greater the force
How would you investigate floating and sinking?
Give a rough explanation of the investigation you would undertake
What is the general rule for all things that float?
The lighter they are, the more they float and vice-versa
How does water affect the way in which something floats or sinks?
The upthrust
What is the effect of a bigger force on a spring?
The bigger the force, the longer it stretches which means it can be used as a force measurer
Give 2 reasons why a spring is a good force measurer
- It stretches evenly
2. It ‘jumps back’ to its original length when the force is taken away which means it can be used over and over again
What is the name given to the force measurers?
Spring balances
Describe a spring balance - 4 points
- Have springs inside them
- Each spring has a pointer fixed to it
- When force is put on the hook, the spring stretches and the pointer moves over a scale on the balance
- When the pointer stops you can read off the size of the force for the scale
Roughly what will 1 Newton weigh the same as?
A medium-sized apple
What is a spring balance named whose scale is marked in Newtons?
A Newton Balance
Why do things seems to weigh less in water than air?
Because the water pushes up on the object
What does floating depend on?
Volume as well as mass
Why do ships float?
The metal is wrapped around lots of air in the cabins and so it has a huge volume
What happens when a ship sits on water?
It pushes some of the water out of the way - this is called DISPLACEMENT
What does the water want to do when it is DISPLACED by the ship?
It wants to get back to where it was so it PUSHES on the ship.
If it is a push it must be a force.
This force is called an UPTHRUST.
The mass of water displace by a ship must be what?
Equal to or more than the MASS of the ship if it is to float.
Therefore, ships need a huge volume so they can displace a lot of water.
Describe what happens when a ship is lowered into water - 4 points
- It pushes more and more water aside
- The UPTHRUST gets stronger and stronger
- Eventually, the weight of the ship = the weight of the water pushed aside (the UPTHRUST)
- The ship floats
What is a hydrometer?
A device for comparing the UPTHRUST of different liquids - describe how you would make one and be able to draw an accurate diagram
Who was Samuel Plimsoll?
A Member of Parliament from Derby who responded to the concerns of ships lost at sea during the Industrial Revolution and demanded that ships operate within safety limits determined by a ‘LOAD LINE’ on the ship’s hull. This line is called the PLIMSOLL LINE.
What do the following letters mean? TF, F, T, S, W, WNA
TF = Tropical fresh water F = Fresh water T = Tropical salt water S = Salt water in summer W = Salt water in winter WNA = Winter North Atlantic
Give two examples of ‘useful’ friction
- Walking - between shoe and ground
2. Writing - between hand and pencil
Problems with friction - name 4
- Makes movement difficult - anytime you want to move an object, friction can make the job more difficult
- Wastes energy - eg in a car, excess friction means extra fuel needs to be used
- Heats parts - energy that is ‘lost’ to friction in trying to move an object is really turned to heat energy by rubbing parts
- Wears things out - lubrication is used to prevent them from wearing things out as well as make them move easily
What is the relationship between mass and fiction?
The bigger the mass, the greater the friction
