Forces Flashcards
What is a scalar?
A quantity with magnitude but no direction.
What is a vector?
A quantity with magnitude and direction.
What is a contact force?
Two objects touch each other to interact.
What is Newton’s third law of motion?
When two objects interact with each other, they exert equal and opposite forces.
What is Newton’s first law of motion?
If the forces acting on an object are balanced, the resultant force on the object is zero.
What is a moment?
The turning effect of a force.
How do you resolve a force?
- Faint axis, good scale, key.
- Measure angle and draw line to correct length.
- Draw horizontally and vertically to the end of the line.
- Measure both, convert both from key.
How do you do parallelogram forces?
- Draw a line of correct length, good key.
- Draw second force line at given angle of correct length.
- Draw mirrored opposite lines to create the parallelogram.
- Draw a diagonal line through the shape. This is the resolving force. Measure, convert from scale.
What is displacement?
The distance travelled in a given direction.
How do you increase the size of a moment?
- Increase magnitude of the force.
- Increase the perpendicular distance from the line of the force to the pivot.
What does a lever act as?
A force multiplier.
What does a low gear give? Which gear turns which?
A low speed with a high turning effect. A small gear turns a large gear.
What does a high gear give? Which gear turns which?
A high speed with a low turning effect. A large gear turns a small gear.
What does a small gear turning a large gear do?
It gives low speed but a high turning effect (force).
What does a large gear turning a small gear do?
It gives a low speed but a high turning effect (force).
What does the gradient of the line on a distance-time graph represent?
The speed.
What is velocity?
The speed of an object in a given direction.
What is acceleration?
The change in velocity of an object per second.
What does the gradient of a line on a velocity-time graph represent?
Acceleration.
What happens when a resultant force acts on an object?
It accelerates in the direction of the resultant force.
What does Newton’s second law of motion say?
Acceleration is directly proportional to the resultant force and inversely proportional to the mass.
What is the resultant force acting on a falling object?
The force of gravity.
What is terminal velocity?
Where the object is falling fast enough that the drag force becomes equal to the weight of the object. The velocity becomes constant.
How is thinking distance increased?
The driver may be tired, drunk, on drugs or using a mobile phone.
How is braking distance increased?
By poorly maintained roads, bad weather, worn tyres, worn brakes.
Is momentum a vector or scalar?
A vector.
What is the unit for momentum?
Kg m/s
What is the unit for a moment?
Nm
What is a closed system?
A system of objects that has no resultant force acting on it.
What is the law of conservation of momentum?
The total momentum before the interaction of an object is equal to the total momentum after the interaction.
What happens with an explosion with momentum?
One object has positive momentum and one has negative momentum.
How is an impact force calculated?
Force = (mass x change in velocity) / time
Change in momentum = mass x change in velocity
SO
Force = change in momentum / time
What do crumple zones in cars do?
They increase the impact time so the force on the car is reduced.
What do safety features in a car do?
- Seatbelts and airbags spread the impact force across a large area.
- Airbags increase the impact time.
- Seatbelts prevent flinging forward and increases impact time.
- Side impact bars and crumple zones increase impact time.
What is the relationship between extension and force applied? Who’s law is it?
They are directly proportional. This is Hooke’s law.
When may a spring graph line start curving?
When you exceed the limit of proportionality.
The stiffer a spring:
The greater it’s spring constant.
What is the unit for pressure?
Pascals.
How is pressure at a point in a liquid calculated?
Height of liquid x density x gfs
The further you go down in a liquid:
The greater the height, so the greater the pressure.
What is atmospheric pressure due to?
Collisions of air particles with surfaces.
Why does higher altitude mean lower pressure?
The higher the altitude, the less weight of air there is above that altitude, so the lower the pressure.
ALSO
The higher the altitude, the less dense the air is as there are fewer molecules, so the lower the pressure.
How is force experienced by an object under different pressures calculated?
Force = difference in pressure x the area of flat surface
How is upthrust created in water?
The pressure at the bottom of an object is greater than the pressure at the top of the object. So the upward force is greater than the downward force. A resultant force is created.
What is upthrust equal to?
The weight of fluid displaced.
When does an object float?
When it’s weight is equal to the upthrust
How does flotation vary with density?
An object that is less dense than the liquid will float.
An object that is more dense than the liquid will sink.
