Forces (p2) Flashcards
What is meant by a vector quantity?
a quantity with magnitude and direction
What is meant by a scalar quantity?
a quantity with magnitude only
Give 5 examples of vector quantities.
Force, velocity, displacement, acceleration, momentum.
Give 5 examples of scalar quantities.
Speed, distance, mass, temperature, time.
What is a force?
a push or pull that acts on an object due to the interaction with another object.
Is force a scalar or vector quantity?
vector
What are the two types of forces?
Contact and non-contact
What is a contact force?
Forces which act when the object causing the force and the object experiencing the force are touching
What ia a non-contact force?
Forces which act even when the object causing the force and the object experiencing the force are not touching
What is gravity?
The force of attraction between masses.
How are weight and mass different?
Mass is a measure of the amount of matter in an object, so remains the same everywhere.
Weight is a force which acts on an object due to gravity.
A measurement of weight could change with location.
What can be used to measure mass?
A mass balance (balancing scales).
What can be used to measure weight?
A calibrated spring balance (newtonmeter).
Mass and weight are directly proportional. What formula links them?
Weight = mass x gravitational field strength
What is the unit for weight?
Newtons (N).
What is the unit for mass?
kg
What is the unit for gravitational field strength?
N/kg
What is a resultant force?
the overall force acting on an object
How is the resultant force acting on an object calculated?
by adding any forces acting in the same direction, and subtracting any forces acting in opposite directions
When is work done to an object?
when a force moves the object through a distance
What is ‘work done’?
the energy transferred to an object by a force
What equation can be used to find work done?
Work done = force x distance
What unit is equivalent to 1 newton-metre?
1 Joule
What energy store increases when work is done against friction?
thermal store (the object’s temperature increases)
What is elastic deformation?
Where an object returns to its original shape after the force deforming it is removed.
What is inelastic deformation?
Where an object doesn’t return to its original shape after the force deforming it is removed.
What is meant by the limit of proportionality (in the context of springs)?
The point where a spring’s extension stops being proportional to the force applied to it. A plotted graph would become non-linear at this point.
What equation is used to find the force applied to a spring when stretching/compressing it?
F = spring constant x extension
What is the difference between distance and displacement?
Distance is how far an object moves. Distance does not involve direction. Distance is a scalar quantity.
Displacement includes both the distance an object moves, measured in a straight line from the start point to the finish point and the direction of that straight line. Displacement is a vector quantity.
What is velocity?
Speed in a given direction.
What is the difference between speed and velocity?
Speed is how fast something moves. Speed does not involve direction. Speed is a scalar quantity.
The velocity of an object is its speed in a given direction. Velocity is a vector quantity.
What is an average human walking speed?
around 1.5 m/s
What is an average human running speed?
around 3 m/s
What is an average human cycling speed?
around 6 m/s
What is an average value for the speed of sound in air?
around 330 m/s
Descrive the speed and velocity of an object travelling in a circle
motion in a circle involves constant speed but changing velocity
How can you find the speed of an object from a distance-time graph?
calculating the gradient
What is acceleration?
how quickly an object changes its velocity
What equation is used to calculate acceleration?
acceleration = change in velocity ÷ time
What does ‘decelerating’ mean?
an object is changing its speed by slowing down
How can you find the acceleration of an object from a velocity-time graph?
by calculating the gradient
How do objects reach terminal velocity?
An object falling through a fluid initially accelerates due to the force of gravity. Eventually the resultant force will be zero and the object will move at its terminal velocity.
How can you find the displacement of an object from a velocity-time graph?
by finding the area under the line of the graph
What is Newton’s 1st law?
If the resultant force on an object is zero, its motion does not change
What is inertia?
The tendency for objects to continue in their state of rest or in uniform motion (like in Newton’s first law)
What is Newton’s 2nd law?
An object’s acceleration is directly proportional to the resultant force acting on it, and inversely proportional to its mass
What does an object’s inertial mass measure?
How difficult it is to change the object’s velocity.
How would you find an object’s inertial mass?
m = F/a (inertial mass is the ratio of force over acceleration)
What does the symbol ~ mean?
approximately
What is Newton’s 3rd law?
Whenever two objects interact, the forces they exert on each other are equal and opposite.
What is stopping distance?
the distance a vehicle travels during the driver thinking and the driver braking
What is a typical human reaction time?
0.2 - 0.9 seconds
What factors affect a driver’s reaction time?
Tiredness, drugs, alcohol and distractions.
What factors affect braking distance?
poor road conditions (wet or icy), poor weather conditions, poor condition of the vehicle (brakes or tyres)
What happens to energy stores when a vehicle’s brakes are applied?
Work is done by the friction force between the brakes and the wheel which reduces the kinetic energy of the vehicle and increases the thermal store (temperature) of the brakes
Why is applying the brake too hard/quickly dangerous?
Very large decelerations may cause brakes to overheat or loss of control of the vehicle
What is momentum?
A vector quantity which is the product of both an object’s mass and velocity - it can be defined as “mass in motion”.
What equation is used to find an object’s momentum?
momentum = mass x velocity
What is the unit for momentum?
kg m/s
What is the law of conservation of momentum?
In a closed system, the total momentum before an event is equal to the total momentum after the event
