Chapter 2 - Forces Flashcards
What is a force?
A force is a push or pull that can change the shape of an object or change the way that is moves. Forces can slow things down and stop them moving, or speed the objects up. If the object is already moving, then forces can change the direction of motion.
Forces can change the shape, speed, or direction of an object in motion.
What are non-contact forces?
Non-contact forces act even when objects are not touching.
- Gravitational forces act between objects that have mass. This force acts towards the centre of the planet, it attracts the planet to you and you to the planet.
- Electrostatic forces act between objects that are electrically charged. For example, rubbing plastic objects can charge them with static electric. Once charged objects can attract or repel other charged objects.
- Magnetic forces act between magnets, and between magnets and magnetic materials such as iron, steel, or nickel.
What are contact forces?
Contact forces act when objects are touching.
- Frictions acts when solid surfaces are in contact. The force of friction acts to stop objects moving.
- Air resistance/water resistance acts on objects moving through air/water. They are types of drag. The moving object collides with the particles in the air/water, and the collisions slow it down.
- Thrust pushes a car or plane forward.
- Upthrust is the upward force on an object that it is in contact with fluid. It is the force pushing up on any floating object.
- Tension acts when objects are pulled, like the force in a rope that you pull.
- Reaction is the force that pushes you up in reaction to your weight pushing somethings downwards, for examples when you sit on a chair. It is sometimes called the normal force.
How can you measure the size of a force?
You can measure the size of a force through a device for measuring forces called a force meter. A spring balance is an example of a force meter. Forces are measured in units called Newtons (N), so force meters are also called newton meters.
What is gravity?
Gravity is a force of attraction between all objects that have mass. It is pulling you down towards the centre of the Earth. Forces come in pairs - so you are also pulling the Earth to you The size of the force of gravity between two objects depends on the mass of the two objects and how far apart they are.
Compare weight and mass.
Weight is measure of force whereas mass is the measure inertia. The SI unit of weight is Newton (N) and the SI unit of mass is kilogram (kg)
Weight is the measure of gravitational pull on an object whereas mass is the amount of matter in an object. Your weight will vary depending on your location and your mass.
What is inertia?
Inertia is the tendency of an object to resist change in its state of motion. It means an object will continue its current motion until some force causes its speed or direction to change.
What a gravitational field strength?
There is a gravitational field around all objects. This is a region where a mass experiences a force. On the Earth the gravitational field strength is 10 Newtons per kg.
Weight = Mass x Gravitational Field Strength
What is air resistance?
Air resistance is a force that acts upon an object moving through air. It is usually unnoticeable.
An object moving through air collides with the particles in the air and is effectively pushing the air out the way, the collision with the air particles provide the resistance. Air resistance is affected by the speed of the object.
How can we reduce air resistance?
Air resistance is less if the area in contact with the air is small. Streamlining reduces air resistance by changing the flow of air over a car or a plane. Air resistance depends on the speed and the area of the object.
Can air resistance be useful?
Air resistance can be useful for slowing things down. For example, a parachute.
Do heavier objects fall quicker?
Air resistance affects the motion of heavier objects more than the motion of lighter objects. If there is a vacuum then the objects will fall at the same rate.
What is a vacuum?
A vacuum is an area with no air.
What is a centripetal force?
A force that keeps an object moving in a circle is called a centripetal force. For a ball on a wire, the centripetal force comes from tension and for cars on a curved road, the centripetal force comes for the friction between the tires and the road.
It can be provided by forces such as muscular force, tension or gravitational force.
How is centripetal force in space?
You can see centripetal force in space through the way that planets and satellites orbit other planets and the sun.
The centripetal force that keeps the Moon and the satellites in orbit around the Earth is provided by the force of gravity. It is gravity that also keeps the planets and asteroids in about around the sun, and keeps moons in around other planets.
