forces Flashcards
Define scalar quantities
- Quantities that have magnitude only
Define vector quantities
- Quantities that have magnitude and an associated direction
How can a vector quantity be represented?
- By an arrow
- The length of the arrow represents the magnitude
- The direction of the arrow represents the direction of the vector quantity
Examples of scalar quantities
- Distance, mass, speed, time
Examples of vector quantities
- Velocity, displacement, acceleration, force, momentum
What is the difference between scalar and vector quantities?
- Vectors can have direction - can be positive or negative
- Scalars can only be positive
Define a force
- A push or pull that acts on an object due to the interaction with another object
What can all forces between objects be?
- Contact forces; the objects are physically touching
- Non-contact forces; the objects are physically separated
What is the unit of force?
- Newtons (N)
Give examples of contact forces
- Friction, air resistance, tension, normal contact force
Give examples of non-contact forces
- Gravitational force, electrostatic force, magnetic force
What type of quantity is force?
- A vector quantity
How do forces interact between objects?
- There’s an equal but opposite force of attraction between the objects
Define weight
- The force acting on an object due to gravity
Define gravitational field
- The force of gravity close to the Earth
What does the weight of an object depend on?
- The gravitational field strength at the point where the object is
Define the centre of mass
- The single point where the weight of an object may be considered to act
What is the weight of an object directly proportional to?
- The mass of the object
What is used to measured weight?
- A calibrated spring-balance (a newtonmeter)
Define mass
- The quantity that tells us how much matter is within an object
What is the difference between mass and weight?
- Mass is constant no matter where the object is
e.g., if the mass of a person on Earth is 70kg, they will be 70kg in mass no matter where they are in the universe - Weight, however, will vary depending on where the object is (depending on the strength of the gravitational field)
What does a g of 9.8N/kg mean?
- For every kilogram of mass, an object will exert 9.8N of weight downwards onto the earth
Define the resultant force
- The single force that has the same effect as all of the original forces acting on the object (the overall force)
What are the 4 directions in a free-body diagram?
- UP: lift
- DOWN: weight
- LEFT: drag (e.g., air resistance, friction)
- RIGHT: thrust