Physics - Forces Flashcards
What is a Scalar quantity
Scalar quantities have magnitude (size) only
Define vector quantity
Vectors have both magnitude (size) and direction
What is a force?
A push or pull
When are forces contact?
When objects are touching
When are forces non-contact?
When objects are not touching
Give an example of a contact force
Friction, air resistance, tension and normal contact force
Given an example of a non-contact force
Gravitational force, electrostatic force and magnetic force
What is weight?
The force acting on an object due to gravity.
What is mass?
The amount of matter in an object.
What is the equation linking weight, mass and gravitational field strength?
Weight = mass x gravity
What is used to measure weight?
Newtonmeter
Where does the weight of any object act from?
Centre of mass
What is a resultant force?
A single force to represent multiple forces
How do you calculate a resultant force?
Take away (opposite directions) or add (same direction) the forces.
When is work done on an object?
When a force moves it a distance.
What is equation linking work done, force and distance?
Work done = force x distance
How many Joules is one Newton-metre?
1 joule
What happens to the temperature of an object when work is done against friction?
It increases
What happens to an elastic object up to the limit of proportionality?
Elastic deformation (It is able to return to its original length)
What happens to an elastic object after the limit of proportionality?
Inelastic deformation (It will not return to its original length)
What is the relationship between force and extension for an elastic object?
Directly proportional
What is equation linking force, the spring
constant and extension?
Force = spring constant x extension
Is distance a scalar or vector quantity?
Scalar
Is displacement a scalar or vector quantity?
Vector
Is speed a scalar or vector quantity?
Scalar
Is velocity a scalar or vector quantity?
Vector
What is displacement?
Both distance and Direction
What is the typical value of walking speed?
1.5 m/s
What is the typical value of running speed?
3 m/s
What is the typical value of cycling speed?
6 m/s
What is the equation linking distance, velocity and time?
distance = speed x time
When moving in a circle at constant speed, why is velocity constantly changing?
Direction changes, velocity is a vector
How do you calculate the speed of an object from a distance time graph?
by calculating the gradient
How do you calculate the distance travelled from a velocity-time graph?
Calculate the area under the curve/line of the selected time
How do you calculate acceleration from a velocity-time graph?
by calculating the gradient
What is acceleration?
The change in velocity over a given period of time
What is the equation linking acceleration, change of in velocity and time?
acceleration = change in velocity ÷ time
If an object is falling due to gravity what acceleration does it have?
9.8 m/s 2
What is the name for the constant speed a falling object reaches when the resistive force is equal to its weight?
Terminal velocity
What does Newtons first law say?
The velocity of an object will only change if there is a resultant force
Describe the motion of an object that is initially stationary, when the resultant force is zero
Remains stationary
Describe the motion of an object that is initially moving, when the resultant force is zero
Continues to move a constant speed in the same direction
What do we call the tendency of an object to remain in a steady state? (H)
Inertia
According to Newtons second law, what is the
acceleration of an object inversely proportional to?
mass
What is the equation linking force, mass and acceleration?
Force = mass x acceleration
What is the inertial mass of an object? (H)
how difficult it is to change the velocity of an object
What is Newtons third law?
When two objects interact they exert equal and opposite forces on each other
What is stopping distance?
Thinking distance + braking distance
What is thinking distance?
distance travelled during reaction time
What is braking distance?
distance travelled once the brakes have been applied
What is a typical reaction time?
0.2 to 0.9 s
Give some factors that can affect reaction time
tiredness, drugs and alcohol, poor visibility
Give some factors that can affect braking distance
speed, worn tyres, worn brakes, icy roads, damaged roads
What is the law of conservation of the momentum?
total momentum before = total momentum after
What is equation linking the momentum, mass and velocity?
momentum = mass x velocity
Define Spring constant.
The stiffness of the spring
When moving in a circle in constant speed, why is velocity constantly changing?
Although the speed remains constant, direction changes, and since velocity is a vector quantity velocity changes
State Newton, second law
The resultant force acting on an object will cause the object to accelerate in the direction of this force
According to Newton’s second law, what is the acceleration of an object proportional to?
The resultant force
State three properties of a pair of forces which obey Newton’s third law
The forces are the same type, they act of two different bodies and have the same line of action
How is the force acting on an object related to its momentum?
Force = rate of change of momentum
How do safety, features such as air bags and seatbelts, reduce forces
Increase the time taken for the change of momentum
What is a moment?
Turning affect of a force
What is the equation linking moments, force and distance?
Moment of a force = force x distance
Describe the moment when an object is balanced
Clockwise moment. = anticlockwise moment.
How does a lever reduce the amount of force needed to create a moment?
By increasing the distance from the pivot
What is a fluid?
A liquid or a gas
What does pressure in a fluid cause?
A force at right angles to any surface
What is the equation linking pressure force and area?
Force = pressure x area
What is the equation, linking pressure, height, density and gravitational field strength
Pressure = height of the column x density of the liquid x gravitational field strength
Describe upthrust in terms of pressure
Pressure on bottom surface is greater than the pressure on the top surface
What happens to the density of the atmosphere with increasing altitude?
It decreases
What creates atmospheric pressure?
Collisions from air molecules
Why does atmospheric pressure decrease with high above ground?
Less air above as the height increases