Section 4: Mechanics Flashcards
What is Newton’s 1st Law of motion?
“The velocity of an object will not change unless a resultant force acts upon it.”
State the principle of moments.
For a body to be in equilibrium, the sum of the clockwise moments about a point equals the sum of the anticlockwise moments. The resultant force will be 0.
What is Lift? When does it occur? And what direction does it act?
Lift is an upwards force on an object moving through a fluid. It happens when the shape of an object causes the fluid flowing over it to change direction. The force acts perpendicular to the direction in which the fluid is flowing.
What causes objects to topple?
If the line of action of its weight falls outside its base area. This is because a resultant moment will occur causing it to fall away from its original position.
What is meant by the centre of mass of an object?
The single point that you can consider its whole weight to act through. An object will balance around this point. For a uniform solid, this will be at the centre of the object.
What is meant by freefall?
When there’s gravity acting on an object and nothing else. Defined as the motion of an object undergoing an acceleration of ‘g’.
What are the conditions needed for a body to be in equillibrium?
All forces acting on the object must be balanced - the resultant force must be 0. An object in equilibrium will be at rest or at a constant velocity.
What is friction? What three important things relate to friction?
Friction is a force that opposes motion.
1) Friction forces always act in the opposite direction to the motion of the object.
2) They can never speed things up or start something moving.
3) They convert kinetic energy into heat.
What is terminal speed?
Terminal speed is the maximum velocity a free falling object will reach, it happens when frictional forces equal the driving force. The resultant force will be 0, therefore the resultant acceleration will also be 0.
What is the principle of conservation of energy?
Energy cannot be created or destroyed. Energy can be transferred from one form to another but the total amount of energy in a closed system will not change.
Give 5 examples of vector quantities
1) Displacement 2) Velocity 3) Force 4) Acceleration 5) Momentum
What is the principle of linear momentum?
Assuming no external forces act, linear momentum is always conserved. This means the total linear momentum of two objects before they collide equals the total linear momentum after the collision.
What is a projectile and why does it follow a curved path?
Any object given an initial velocity and then left to move freely under gravity is a projectile. The horizontal and vertical components of the motion are completely independent. They follow a curved path because the horizontal velocity remains constant, while the vertical velocity is affected by the acceleration due to gravity - ‘g’.
What is Impulse? How do you find it from a force - time graph?
The change in momentum. Area under the graph.
What is Newton’s Third law?
If object A exerts a force on object B, then object B exerts an equal but opposite force on object A.
How would you work out the Moment of a couple?
What is meant by Displacement, Velocity and Acceleration?
Displacement - How far an object’s travelled from its starting point in a given direction
Velocity - The rate of change of an objects displacement
Acceleration - The rate of change of an object’s velocity
How does air resistance affect projectile motion?
The horizontal component of drag reduces the horizontal speed of the projectile, and reduces the horizontal distance the projectile can travel. The vertical component of drag reduces the maximum height the projectile will reach, and steepens the angle of descent.
How would you find the centre of mass of an object by experiment?
1) Hang the object freely from a point
2) Draw a vertical line downwards from the point of suspension
3) Hang the object from a different point and draw another vertical line
4) The centre of mass is where the two lines cross
How do you calculate average velocity from a displacement-time graph?
The average velocity is just the total change in displacement of the object divided by the total time taken.
What is drag? What main three things affect fluid friction?
Drag is friction due to a fluid.
1) The force depends on the thickness of the fluid.
2) The force increases as the speed of the object increases.
3) The force depends on the shape of the object moving through it - larger area pushing against the fluid, the greater the resistance force.
What two ways can you increase the top speed of a vehicle travelling through a fluid.
1) Increasing the driving force, e.g by increasing the engine size.
2) Reducing the frictional force, e.g making the body more streamlined.
Give 6 examples of scalar quantities
1) Length
2) Speed
3) Mass
4) Temperature
5) Time
6) Energy
Define a couple.
A couple is a pair of forces of equal size which act parallel to each other, but in opposite directions. A couple doesn’t produce any resultant linear force, but does produce a turning effect.
