How is force mass and acceleration related

Scientists measure force in units called newtons, where one newton is the force needed to accelerate a 1-kilogram mass one meter per second squared.

Acceleration comes only from a change in speed. When an object gains speed, its acceleration is positive; when speed is lost, acceleration is negative. You measure speed in units of distance divided by time, such as miles per hour or meters per second. Acceleration is the change in speed divided by the time the speed takes to change, so it is meters per second per second, or meters per second squared. The mass of an object is a measure of how much matter it contains. A rubber ball has less mass than a lead ball of the same size because it has less matter in it, fewer atoms and fewer of the protons, neutrons and electrons that make up the atoms.

Mass also resists the effort to push or pull it; a ping-pong ball is easy to pick up and toss; a garbage truck is not. The truck is more massive than the ping-pong ball by many thousands of times. The standard unit for mass is the kilogram, about 2. Mass is a simple kind of quantity. You can have large masses, tiny masses and in-between masses. Scientists call simple quantities scalars because one number will describe it. Force and acceleration, however, are more complicated.

This provides sharper pictures than with a disc stroboscope, provided that you have a good blackout. General guidance is as for Method 3. Direct the light from the stroboscope along the pathway of the object.

In multiflash photography, avoid flash frequencies in the range Hz, and avoid red flickering light. Some people can feel unwell as a result of the flicker. Rarely, some people have photosensitive epilepsy.

Classroom management in semi-darkness. Use a white or silver object, such as a large, highly polished steel ball or a golf ball, against a dark background. Alternatively, use a moving source of light such as a lamp fixed to a cell, with suitable electrical connections. In this case, place cushioning on the floor to prevent breakage. Place a measured grid in the background to allow measurement. A black card with strips of white insulating tape at, say, 10 cm spacing provides strong contrast and allows the illuminated moving object to stand out.

As an alternative to the grid, you can use a metre rule. Its scale will not usually be visible on the final image, but you can project a photograph onto a screen.

Move the projector until the metre rule in the image is the same size as a metre rule held alongside the screen. You can then make measurements directly from the screen.

Make sure that any system is as rigid and stable as possible. Teamwork matters, especially in Method 3. One person could control the camera, another the stroboscope system as necessary, and a third the object to be photographed.

The first law describes what happens when the forces acting on a body are balanced no resultant force acts — the body remains at rest or continues to move at constant velocity constant speed in a straight line. If a book is placed on a table, it stays at rest. There are two forces on the book and they happen to balance owing to the elastic properties of the table.

The table is slightly squashed by the book and it exerts an elastic force upwards equal to the weight of the book. You can show this by placing a thick piece of foam rubber on a table and placing a book on top of it. The foam rubber squashes. Galileo was the first person to challenge the common sense notion that steady motion requires a steady force.

He looked beyond the obvious and was able to say if there was no friction then an object would continue to move at constant velocity. In other words, he put forward a hypothesis.

He could see that a motive force is generally needed to keep an object moving in order to balance frictional forces opposing the motion. The motion of air molecules is a good example to consider with students. When air temperature is constant, no force is applied to keep air molecules moving, yet they do not slow down.

If they did, in a matter of minutes the air would condense into a liquid. The second law describes what happens when the forces acting on a body are unbalanced a resultant force acts. The body changes its velocity, v , in the direction of the force, F , at a rate proportional to the force and inversely proportional to its mass, m. And rate of change of velocity is acceleration, a.

So if the table mentioned above were in an upwardly accelerated lift, an outside observer would see that the two forces acting on the book were unequal.

The resultant force would be sufficient to give the book the same upward acceleration as the lift. Put some bathroom scales between the book and the table. If the book is accelerating downwards, its weight would be greater than the reaction force from the table.

The book would, however, appear to be weightless. Newton wanted to understand what moves the planets. He realized that a planet requires no force along its orbit to move at constant speed, but it does require a force at right angles to its motion gravitational attraction to the Sun to constantly change direction.

Many students find this law the most difficult one to understand. Returning to the book on a table, there are three bodies involved: the Earth, the book, and the table. In this example, the interaction pairs of forces are:. If the constant is equated to unity, then we are defining a unit of force. Solid carbon dioxide is known as dry ice. It is often used in theatres or nightclubs to produce clouds looking a bit like smoke. Because it is denser than the air, it stays low. It cools the air and causes water vapour in the air to condense into tiny droplets — hence the clouds.

Dry ice can be dangerous if it is not handled properly. Wear eye protection and gauntlet-style leather gloves when making or handling solid carbon dioxide. Dry ice has many uses. As well as simply watching it sublime, you could also use it for cloud chambers, dry ice pucks, and cooling thermistors and metal wire resistors in resistance experiments.

It can also be used in experiments related to the gas laws. It is possible to make the solid snow by expansion before the lesson begins and to store it in a wide-necked Thermos flask. Remember that the first production of solid carbon dioxide from the cylinder may not produce very much, because the cylinder and its attachments have to cool down.

This enables you to extract from the cylinder bottom so that you get CO 2 in its liquid form, not the vapour. NOTE: A plain black finish to the cylinder indicates that it will supply vapour from above the liquid. A cylinder with two white stripes, diametrically opposite, indicates it has a siphon tube and is suitable for making dry ice.

The refill charge can be reduced by having your chemistry department cylinders filled up at the same time. The bold letters F and a in the equation indicate that force and acceleration are vector quantities, which means they have both magnitude and direction.

The force can be a single force or it can be the combination of more than one force. It is rather difficult to imagine applying a constant force to a body for an indefinite length of time. In most cases, forces can only be applied for a limited time, producing what is called impulse. For a massive body moving in an inertial reference frame without any other forces such as friction acting on it, a certain impulse will cause a certain change in its velocity.

The body might speed up, slow down or change direction, after which, the body will continue moving at a new constant velocity unless, of course, the impulse causes the body to stop. There is one situation, however, in which we do encounter a constant force — the force due to gravitational acceleration, which causes massive bodies to exert a downward force on the Earth. Notice that in this case, F and g are not conventionally written as vectors, because they are always pointing in the same direction, down.

The product of mass times gravitational acceleration, mg , is known as weight , which is just another kind of force.