Topic 5 - Forces Flashcards
What is acceleration?
The rate of change of velocity. It can be calculated from the gradient of a velocity-time graph.
What is the definition of atmosphere?
The thin layer of air surrounding the Earth, which gets less dense
with increasing altitude.
What is braking distance?
The distance a vehicle travels under the braking force. This can be affected by adverse road and weather conditions as well as the condition
of the vehicle.
What is centre of mass?
The single point through which the weight of the object can be said to act.
What are changes in momentum?
When a force acts on a moving object, or one an
object that has the ability to move, a change of momentum will occur. The
force is equal to the rate of change of momentum.
What is the conservation of momentum?
The total momentum of a system before an event is always equal to the total momentum of the system after the event.
What are contact forces?
A force that occurs when objects are physically touching.
What is displacement?
A measure of how far an object moves in a given direction. It is the straight line between the starting and finishing points and is a vector quantity.
What is distance in physics?
A measure of how far an object moves, that does not depend on direction and is therefore a scalar quantity.
What is elastic deformation?
Non-permanent deformation which allows the object to return to its original shape when the deforming forces are removed.
What is elastic limit?
The force beyond which an object will no longer deform elastically, and will instead deform plastically.
What is elastic potential energy?
The energy stored in a spring when it is stretched or compressed, due to the work done on the spring by the deforming force. It is equal to the work done as long as the object does not plastically deform.
What is equilibrium?
An object is in equilibrium if the resultant force and resultant moment are both equal to zero.
What does floating mean in physics?
An object will float if the volume of liquid it displaces has a greater weight than that of the object itself. The upthrust acting on the object is greater than its weight.
What is a fluid?
A liquid or gas.
What are forces?
A push or pull that an object experiences due to the interaction with another object. Force is a vector quantity.
What is Inertia?
The tendency of an object to remain in its same state of uniform motion or rest.
What is inertial mass?
A measure of how hard it is to change an object’s velocity. It is defined as the ratio of force over acceleration.
What is limit of proportionality?
The point beyond which the extension of an elastic
object is no longer directly proportional to the force applied to it.
What is moment?
The turning effect of a force, equal to the product of the magnitude of the force and the perpendicular distance from the pivot to the line of action of the force.
What is momentum?
The product of an object’s mass and velocity.
What is a newton meter?
A calibrated spring-balance used to measure weight.
What is Newton’s first Law?
If a stationary object’s resultant force is zero, the object will remain stationary. If a moving object’s resultant force is zero, the object will
continue to move at the same speed, and in the same direction.
What is Newton’s second Law?
An object’s acceleration is directly proportional to the
force applied to it, and inversely proportional to its mass.
What is Newton’s third Law?
The forces that two objects exert on each other when they interact are equal and opposite.
What are non contact forces?
A force that occurs when objects are physically separated.
What is plastic deformation?
Permanent deformation which means the object will no longer return to its original shape when the deforming forces are removed.
What is pressure in a column?
The pressure in a column of liquid is equal to the product of the liquid’s density, the height of the column and the gravitational field strength.
What is resolution of forces?
All forces can be resolved into two perpendicular
components that have the same effect as the single force.
What is a resultant force?
The single force that can replace all the individual forces acting on an object, and have the same effect.
What is resultant moment?
The single moment that has the same effect as the sum of all the other clockwise and anticlockwise moments acting on an object.
What are scalar quantities?
Quantities that only have a magnitude, not a direction.
What does sinking mean?
An object will sink if the volume of liquid it displaces has a lower weight than that of the object itself. The upthrust acting on the object is lower than its weight and so there is a resultant downwards force.
What is speed?
A scalar quantity that is a measure of the rate of increase of distance.
What is a spring constant?
A measure of a spring’s stiffness, which is the constant of proportionality for a spring’s extension. The higher the spring constant, the smaller the extension is for a given force.
What is stopping distance?
The sum of the thinking and braking distances.
What is thinking distance?
The distance a vehicle travels during the driver’s reaction time. Typical human reaction times are in the range of 0.2-0.9 seconds. This reaction time may be affected by tiredness, drugs or alcohol.
What is upthrust?
The upward force acting on an object in a fluid, due to it
experiencing a greater pressure below it than above it.
What are vector quantities?
Quantities that have both a magnitude and direction. They are represented by an arrow, with the length representing the magnitude and the arrowhead representing the direction.
What is velocity?
A vector quantity that is a measure of the rate of change of displacement. It is the speed in a given direction.
What is weight?
The force acting on an object due to gravity. It is equal to the product of the object’s mass and the gravitational field strength at its location.
What is work done?
Work is done on an object when a force causes it to move through a distance. It is directly proportional to the distance travelled and the magnitude of the force in the direction of motion.
What piece of equipment can be used to measure an object’s weight?
A calibrated spring balance or newton meter.
Under what circumstance is 1 joule of work done?
When a force of 1 newton causes a displacement of 1 meter.
How many newton metres are equal to 1 joule of energy?
1 Nm = 1 J
Why does air resistance slow down a projectile?
- The object does work against the air resistance
- Kinetic energy is converted into heat, slowing down the object
What is meant by an inelastic deformation?
- A deformation which results in the object being permanently stretched
- The object doesn’t return to it’s original shape when the force is removed
What three part make up a lever system?
- Load
- Effort
- Pivot
What determines the moment of a gear wheel?
The size of the wheel.
Describe the moment and speed of a larger gear being driven by a smaller gear?
The larger wheel will rotate more slowly but will also produce a larger moment.
In any fluid, at what angle do the forces due to pressure act on a given surface?
At right angles to the surface.
If an object moves 3 metres to the left and then 3 metres back to it’s initial position, what is the object’s total displacement?
- The object has zero displacement
- Displacement is a vector quantity so it also involves direction
- The object starts and end at the same point
State a typical value for the speed of sound?
330 m/s
What is a typical value for human walking speed?
1.5 m/s
What is a typical value for human running speed?
3 m/s
What is a typical value for human cycling speed?
6 m/s
Why can an object travelling at a constant speed in a circle not have a constant velocity?
- Speed is a scalar quantity
- Velocity is a vector quantity which mean it can only be constant if the direct is constant
- In circular motion, the direction continuously changing
What must be done to calculate speed at a give n time from a distance- time graph for accelerating object?
- Drawing a tangent to the curve at the required time
- Calculating the gradient of the tangent
State Newton’s first law for a stationary object.
If the resultant force on a stationary object is zero, the object will remain at rest.
State Newton’s first law for a moving object.
If the resultant force on a moving object is zero, the object will remain at constant velocity.
What is inertia?
The tendency of an object to continue in it’s state of rest or uniform motion.
State the defining equation for Newton’s second law.
Resultant Force = Mass x Acceleration
F= MA
What is inertial mass?
- A measure of how difficult it is to change a given object’s velocity
- The ratio of force over acceleration
State Newton’s Third Law.
Whenever two objects interact, the forces that they exert on each other are always equal and opposite.
Give a typical range of values for human reaction time.
0.2 - 0.9 Seconds
Give three factors which can affect a driver’s reaction time.
- Tiredness
- Drugs
- Alcohol
Explain how a seatbelt improves a passenger’s safety during a collision.
- Passenger must decelerate from the vehicle’s velocity at impact to zero, meaning they undergo a fixed change of momentum.
- The force they experience is equal to the rate of change of momentum
- Seatbelts increase the time over which the face is applied, reducing the rate of change of momentum and therefore reducing the force experienced.
