During the movement of an object, the ratio of the change of its speed to the time taken for the change is calledacceleration(denoted by a).If an object followsRectilinear motion, and the acceleration remains unchanged in the process of motion, then the object is said to be in uniform acceleration linear motion.Its acceleration is a fixed value. When the fixed value is constant zero, it will become a uniform linear motion or static.It can be said that uniform linear motion is a special case of uniformly accelerated linear motion.But in the middle school examination, the uniform linear motion is generally not regarded as the uniform acceleration linear motion.
stayRectilinear motionThe motion in which the magnitude and direction of acceleration do not change (when the acceleration and speed direction are the same) is called uniform acceleration linear motion.
acceleration
During the movement of an object, the ratio of the change of its speed to the time taken for this change is called acceleration (expressed in a, in M/S ^ 2; read as meters per second to the second power), which meansparticleThe physical quantity of speed change is a vector, which has both size and direction.Note: Although acceleration represents object movementSpeed changeThe ratio to the time taken for this change, but it is not determined by the speed and time of the object, but byMass of objectAnd the external force on the object. The acceleration is equal to the ratio of the external force on the object to the mass of the object, that is, a=F/m.
Uniform speed straight line
Acceleration is a vector with magnitude and direction. Suppose an object moves in a certain directionInitial velocityIs the motion of V. If the acceleration direction is the same as the initial velocity direction and the value is a constant greater than 0 in the process of motion, the object is said to be in a uniformly accelerated linear motion.If the acceleration direction is opposite to the initial velocity direction and the value is a constant greater than 0, the object is said to beStraight motion with uniform deceleration(Note that if the acceleration of an object in uniform deceleration motion remains unchanged, it will become stationary at a certain point in time, and then move in the opposite direction in a uniform acceleration straight line with an initial speed of 0).If the acceleration is always 0 in the process of motion, the object willUniform linear motion。It can be said that uniform linear motion is a special case of uniformly accelerated linear motion.
Uniform acceleration condition
There are two cases when an object moves with uniform acceleration: 1. When the object starts to be at a standstill, and the magnitude of the resultant external force is unchanged, and the direction is unchanged, the object moves with a uniform acceleration straight line with an initial speed of 0 along the direction of the resultant force;2. If the object starts to move along a certain direction with an initial speed of V, and the resultant force is unchanged, the direction is the same as the moving direction of the object, then the object will move in a uniformly accelerated straight line with an initial speed of V.(Note that if the direction of the external force on the object is the same as that of the objectInitial velocityIf the direction is opposite and the size is the same, the object starts to decelerate evenly until it is still and then moves along the direction of the resultant force with an initial speed of 0Uniform accelerationSports).
experimental study
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[Purpose and Requirements] UnderstandMagnetic control electronic stopwatchDuring its working process, it will be used to carry out some simple mechanical experiments with the rail car.
[Instruments and equipment]
Inclined trolley (J2108 type), heavy object, magnetic control electronic stopwatch (including two magnetic switches and oneliquid crystalDisplay electronic stopwatch with timing accuracy of 0.01 seconds), smallPermanent magnet4,a scale。
[Experimental method]
(1) Judgment of objects moving in a straight line with uniform acceleration
Confirm that the trolley is working on the flat plateUniform linear motionThen, put a small weight into the weight pan.Fix a magnet on the trolley.The first magnetic switch shall be placed at the position where the trolley starts to move (this position shall remain unchanged and generally be far away frompulleyTo ensure that the trolley has enough movement range), and the second magnetic control switch is placed in the center of the panel.As soon as the car starts moving, it acts on the first magnetic switch to make the stopwatch start timing. After passing the second magnetic switch, the stopwatch stops timing, displays the time t1 from the car's static movement to the second magnetic switch, and measures the distance S1 between the two magnetic switches.
Change the position of the second magnetic switch, repeat the above experiment (pay attention to keep the position where the trolley starts to move and the position of the first magnetic switch unchanged), and obtain the corresponding t2S2、t3、S3、……。
Compare S1/t12S2/t22、S3/t23、……，If they are equal within the experimental error range, the trolley will move in a straight line with uniform acceleration and zero initial speed.
(2) Determination of object acceleration
① Calculate the corresponding acceleration value from Sy Sx=(y-x) aT ², and then take their average value to get the acceleration value of the trolley in the whole movement process.
② At S － t2Coordinate systemDraw points (), (), ()... and make a straight line through these points (points not on the straight line should be evenly distributed on both sides of the straight line). The straight line should pass through the origin (0, 0).Measure the linear and horizontal axisincluded angle, then the motion acceleration of the trolley is
Selected from: High School Physics Student Experiment
Related formula
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Basic formula
Speed formula: V=V0+at (since V0 and a are fixed values, V is about tLinear function)
Velocity of displacement midpoint: vs/2=(2v1v2)/(v1+v2)=√ ((v0 ^ 2+vt ^ 2)/2) v1 v2 is the displacement velocity of the previous section and the displacement velocity of the next section respectively
Acceleration formula in special equal time interval: a=(Sm Sn)/(m-n) t ^ 2 (Sm Sn represents the displacement difference between m and n)
The acceleration formula of adjacent displacement in special equal time interval: a=△ S/t ^ 2 (△ S represents the change of displacement before and after)
V0 vt is the initial speed and the final speed respectively
Δ x=aT ^ 2 (application: timing timer, etc.)
Proportional formula for uniformly accelerated linear motion with initial speed of 0:
1: At the end of T, 2T, 3T...... NT time,Instantaneous velocityRatio 1:2:3:............: n
