Science - Forces Flashcards
(20 cards)
What are forces?
- A force can be a push or a pull.
- For example, when you push open a door you have to apply a force to the door. You also have to apply a force to pull open a drawer.
- You cannot see a force but often you can see what it does.
What can forces do?
- Change speed, direction or shape of an object.
- For example, when you pull on an elescatic band it changes shape.
Measuring forces
- Forces are measured in Newtons using a forces meter (Newton Meter)
- The unit of force is called ‘N’
What is MASS?
- The mass of an object is the amount of matter or “stuff” it contains.
- The more matter an object contains, the greater its mass. e.g An elephant contains more matter than a mouse, so it has a greater mass.
- Mass is measured in kilograms, kg, or grams, g.
What is Gravity?
- The force that attracts objects towards each other.
When does gravity increase?
- When the mass of an object increases AND when objects are closer together.
What is weight?
- It is a FORCE caused by gravity.
- The weight of an object is the gravitational force between the object and the Earth.
- The more mass the object has the greater its weight will be.
Why do you weigh less on the Moon than on Earth?
- The Moon has less mass than the Earth, so its gravity is less than the Earth’s gravity.
- This means that objects weigh less on the Moon than they do on the Earth.
What is the Moon’s gravity compared to Earth?
- The Moon’s gravity is one sixth of the Earth’s gravity. A 120 kg astronaut weighs 1200 N on Earth.
- On the Moon they would weigh only 200 N.
- The astronaut’s mass is 120kg wherever they are.
How do we work out ‘pressure’?
- Weight or Force applaied and area over which the force works.
How do we measure pressure?
- Pressure = FORCE (divided by) AREA
- e.g A force of 20 N acted over an area of 2 m2 (two square metres) = 20 ÷ 2 = 10 N/m2
Force diagrams
- We can show the forces acting on an object using a force diagram.
- Each force is shown as a force arrow.
- An arrow shows: the size of the force (the longer the arrow, the bigger the force) the direction in which the force acts.
What do we mean by ‘balanced forces’?
- When two forces acting on an object are equal in size but act in opposite directions, we say that they are balanced forces.
What happens if the forces on an object are balanced?
- An object that is not moving stays still.
- An object that is moving continues to move at the same speed and in the same direction.
What is an unbalanced force?
- When two forces acting on an object are not equal in size, we say that they are unbalanced forces.
What happens if the forces are unbalanced?
An object that is not moving starts to move. (e.g a person in a car) An object that is moving changes speed or direction. (e.g when you apply brakes in a car)
What is frictional force?
- When an object movers against another object.
Examples of HELPFUL frictional forces.
- Friction between our shoes and the floor stop us from slipping
- Friction between tyres and the road stop cars from skidding
- Friction between the brakes and wheel help bikes and cars slow down
What is ‘air resistance’?
- Air resistance is caused by the frictional forces of the air against a vehicle / object e.g car.
What is TENSION and COMPRESSION?
http://www.youtube.com/watch?v=c-V_8_qmJbE
TENSION is when you stretch material
COMPRESSION is when you push / squeeze material
