1.2.1 - 1.2.9 - Forces, Movement and Changing Shape Flashcards
How can forces affect different bodies?
Changes in speed: forces can cause bodies to speed up or slow down
Changes in direction: forces can cause bodies to change their direction of travel
Changes in shape: forces can cause bodies to stretch, compress, or deform
What are the different type of forces?
Gravitational (or weight) - the force between any two objects with mass (like the Earth and the Moon)
Electrostatic - the force between any two objects with charge (like a proton and an electron)
Thrust - the force pushing a vehicle (like the push from rocket engines on the shuttle)
Upthrust - the upward force on any object in a fluid (like a boat on the surface of a river)
Air resistance (or drag) - the force of friction between objects falling through the air (like a skydiver in freefall)
Compression - forces that squeeze an object (like squeezing a spring)
Tension - forces that stretch an object (like two teams in a tug-of-war)
Reaction force - the force between any two objects in contact (like the upwards force from a table on a book)
What are the two quantities of forces?
All quantities can be one of two types:
A scalar
A vector
What is a scalar?
Scalars are quantities that have only a magnitude
For example, mass is a scalar quantity since it is a quantity that has no direction to it
What is a vector?
Vectors have both a magnitude and a direction
Velocity is a vector quantity since it is described with both a magnitude and a direction
What type of quantity are distance and displacement?
Distance is a value describing only how long an object is or how far it is between two points - this means it is a scalar quantity
Displacement on the other hand also describes the direction in which the distance is measured - this means it is a vector quantity
What are the different scalars and vectors quantities?
What quantity is force?
Force is a vector quantity because it describes both magnitude and direction
The length of the arrow represents the magnitude of the force
The direction of the arrow indicates the direction of the force
What is a resultant force?
A resultant force is a single force that describes all of the forces operating on a body
When many forces are applied to an object they can be combined (added) to produce one final force which describes the combined action of all of the forces
What does a resultant force determines?
The direction in which the object will move as a result of all of the forces
The magnitude of the final force experienced by the object
The resultant force is sometimes called the net force
How can the resultant force be calculated?
Resultant forces can be calculated by adding or subtracting all of the forces acting on the object
Forces working in opposite directions are subtracted from each other
Forces working in the same direction are added together
What is friction?
The force which opposes the motion of an object
Frictional forces always act in the opposite direction to the object’s motion
Friction emerges when two (or more) surfaces rub against each other
What is a balanced force?
Balanced forces mean that the forces have combined in such a way that they cancel each other out and no resultant force acts on the body
What is an unbalanced force?
Unbalanced forces mean that the forces have combined in such a way that they do not cancel out completely and there is a resultant force on the object
What is the link between unbalanced forces, mass and acceleration?
When forces combine on an object in such a way that they do not cancel out, there is a resultant force on the object
This resultant force causes the object to accelerate
The object might speed up
The object might slow down
The object might change direction
What is eq. for Force?
Force = Mass x acceleration
What is weight?
The force acting on an object due to gravitational attraction
Planets have strong gravitational fields
Hence, they attract nearby masses with a strong gravitational force
What effects does weight have?
Objects stay firmly on the ground
Objects will always fall to the ground
Satellites are kept in orbit
What is the eq. for weight?
Weight = mass x gravitational field strength
What does the weight of an object depend on?
The object’s mass
The mass of the planet attracting it
Mass is related to the amount of matter in an object
Weight is the force of gravity on a mass
The weight of an object and the mass of an object are directly proportional
The size of this force depends on the gravitational field strength
What is stopping distance?
The total distance travelled during the time it takes for a car to stop in response to some emergency
What is the eq. for stopping distance?
Stopping distance = Thinking distance + Braking distance
What is Thinking distance, Braking distance and stopping distance?
Thinking distance = the distance travelled in the time it takes the driver to react (reaction time) in metres (m)
Braking distance = the distance travelled under the braking force in metres (m)
Stopping distance = the sum of the thinking distance and braking distance, in metres (m)
For a given braking force, the greater the speed of the vehicle, the greater the stopping distance
What are the factors affecting stopping distance?
Vehicle speed - the greater the speed, the greater the vehicle’s braking distance will be (because the brakes will need to do more work to bring the vehicle to a stop)
Vehicle mass - a heavy vehicle, such as a lorry, takes longer to stop
Road conditions - wet or icy roads make it harder to decelerate
Driver reaction time - a driver’s thinking distance depends on their reaction time. Being tired, or intoxicated (i.e. alcohol, or drugs) can increase reaction time