P8,P9, P10 Flashcards
Displacement
Distance without a change of direction
Vector quantities
Physical quantities with a size and direction
Examples of vectors
Acceleration, force, momentum, weight, gravitational field strength
Scalar quantities
Physical quantities with size, but no specific direction
Examples of scalar quantities
Speed, distance, time, mass, energy, power
Force
A push or pull that acts on an object because of its interaction with anotjer object
Contact forces
Forces if two objects must touch each other to interact e.g. friction, air resistance, stretching forces(tension) and normal contact forces
Non-contact forces
Magnetic force, electrostatic force and the force of gravity
Newton’s third law of motion
When two objects interact with each other, they exert equal and opposite forces on each other
Resultant force
A single force that has the same effect as all the forces acting on the object
Newton’s first law of motion
If the forces acting on an object are balanced, the resultant force on the object is zero, and:
If the object is at rest, it stays stationary
If the object is moving, it keeps moving with the same speed and in the same direction
What is the resultant force if two forces act in the same direction on an object along a straight line?
The resultant force is equal to the sum of the two forces
What does a free-body force diagram show?
The forces acting on an object without any other objects or forces shown
Centre of mass
The point in an object where its mass is thought of as being concentrated
Freely suspended object
When an object returns to its equilibrium position as the turning force is taken away, with the centre of mass directly underneath the point of suspension
How to find the centre of mass in an irregular-shaped card
1) Put a hole in one corner of the card and suspend the card from a rod.
2) Use a plumb line to draw a vertical line on the card from the rod.
3) Repeat the procedure, hanging the card from a different corner.
4) The point where the two lines meet is the centre of mass
Velocity
Speed in a given direction
Is the velocity of an object moving round in a circle constant?
An object moving round in a circle has a direction of motion changes continuously as it goes round, so its velocity’s not constant.
Acceleration of an object
Change in velocity per second
In a velocity time graph, what does the section with a horizontal line show?
Constant velocity
1km/h
0.278m/s
Equation linking constant acceleration and for calculations where time taken isn’t given
v2-u2= 2as
Required practical(investigating force and acceleration)
1) Use the newton-meter to pull the trolley along a known distance with a constant force.
2) A motion sensor and computer can be used to record the velocity of the trolley as it accelerates.
3) Predict what will happen to the acceleration of the trolley is the force is increased/decreased or the mass of the trolley is increased. You can double or treble the total moving mass of the trolley using double-deck and triple-deck trolley.
Safety: Protect your bench and feet from falling trolleys
Resultant force =
Mass x acceleration
Newton’s second law of motion
The acceleration of an object is:
Proportional to the resultant force on the object
Inversely proportional to the mass of the object
Inertia
The tendency of an object to stay at rest or continue in uniform motion(e.g. moving at constant gelocity’
How does the resultant force affect the velocity of an object?
Acceleration- when the resultant force is in the same direction as the velocity
Deceleration - if the resultant force is in the opposite direction to its velocity
Weight
The force acting on an object due to gravity